Typeset Only First n Items or Items after n from a List

Question

I would like to have macro that given splits the text that occurs before a given item count and after a given item count. That is TypesetPartialList[2]{MyList} should typese only the first two items in the list, and the starred variant TypesetPartialList*[2]{MyList} should typeset items except the first two items.

The desired output from the MWE below is

Notes:

You can assume that there is only one list in the parameter to TypesetPartialList.
If the text before and after the list introduces complexities, please assume that the content passed to TypesetPartialList will stricly be a single list.

Code:

documentclass{article}

usepackage{enumitem}
usepackage{xcolor}
usepackage{xparse}

newcommand{MyList}{%
    textcolor{magenta}{This is the text before the list.}
    begin{itemize}
    item 
        This is the textcolor{red}{first} item of the list. 
        There is some additional text so that it occupies at least two lines.
    item 
        This is the textcolor{red}{second} item of the list. 
        There is some additional text so that it occupies at least two lines.
    item 
        This is the textcolor{blue}{third} item of the list. 
        There is some additional text so that it occupies at least two lines.
    item 
        This is the textcolor{blue}{fourth} item of the list. 
        There is some additional text so that it occupies at least two lines.
    item 
        This is the textcolor{blue}{fifth} item of the list. 
        There is some additional text so that it occupies at least two lines.
    end{itemize}%
    textcolor{magenta}{This is the text after the list.}%
}%

NewDocumentCommand{TypesetPartialList}{%
    s%   #1 = star means to typeset items AFTER item number in #2
    O{-1}% #2 = item number to split the list at
    %%          Ex. TypesetPartialList{-1}{<list>} typsets ALL items
    %%              TypesetPartialList{2}{<list>} typsets ONLY items 1 and 2
    %%              TypesetPartialList*{2}{<list>} typsets ONLY items 3 and after
    m%   #3 = list to split
}{%
    #3%
}%

begin{document}
noindenttextbf{First Two Items:}par
TypesetPartialList[2]{MyList}

medskippar
noindenttextbf{Skipping First Two Items:}par
TypesetPartialList*[2]{MyList}
end{document}

lists split

egreg · Answer

It would be much simpler if you remove the text before and after and also the begin{itemize} and end{itemize} tags which you can reinsert when you want to typeset and don't really belong to the list.
I'm not sure what's the purpose of the texts before and after and when they should be output, so I propose a key-value interface for printing them.
documentclass{article}

usepackage{enumitem}
usepackage{xcolor}
usepackage{xparse}

ExplSyntaxOn

NewDocumentCommand{definelist}{ m O{} +m }
 {% #1 = list name
  % #2 = key-value list
  % #3 = list
  grill_lists_define:nnn { #1 } { #2 } { #3 }
 }

NewDocumentCommand{printlist}{ s O{} m O{2} }
 {
  IfBooleanTF { #1 }
   {
    grill_lists_print:nnnn {#4+1} {seq_count:c{ l_grill_lists_#3_seq }} { #3 } { #2 }
   }
   {
    grill_lists_print:nnnn {1} {#4} { #3 } { #2 }
   }
 }

cs_generate_variant:Nn seq_set_split:Nnn { c }
cs_generate_variant:Nn seq_pop_left:NN { c }

keys_define:nn { grill/lists }
 {
  pre  .bool_set:N = l__grill_lists_pre_bool,
  post .bool_set:N = l__grill_lists_post_bool,
  pre  .default:n = true,
  post .default:n = true,
 }
 
cs_new_protected:Nn grill_lists_define:nnn
 {
  prop_clear_new:c { l_grill_lists_#1_prop }
  prop_set_from_keyval:cn { l_grill_lists_#1_prop } { type=itemize, color={.}, #2 }
  seq_clear_new:c { l_grill_lists_#1_seq }
  seq_set_split:cnn { l_grill_lists_#1_seq } { item } { #3 }
  seq_pop_left:cN { l_grill_lists_#1_seq } l_tmpa_tl % discard the empty first item
 }

cs_new_protected:Nn grill_lists_print:nnnn
 {
  group_begin:
  keys_set:nn { grill/lists } { #4 }
  bool_if:NT l__grill_lists_pre_bool
   {
    textcolor{ prop_item:cn { l_grill_lists_#3_prop } { color } }
     {
      prop_item:cn { l_grill_lists_#3_prop } { pre }
     }
   }
  begin{ prop_item:cn { l_grill_lists_#3_prop } { type } } % itemize or ...
  int_step_inline:nnn { #1 } { #2 } { item seq_item:cn { l_grill_lists_#3_seq } { ##1 } }
  end{ prop_item:cn { l_grill_lists_#3_prop } { type } } % itemize or ...
  bool_if:NT l__grill_lists_post_bool
   {
    textcolor{ prop_item:cn { l_grill_lists_#3_prop } { color } }
     {
      prop_item:cn { l_grill_lists_#3_prop } { post }
     }
   }
  group_end:
 }

ExplSyntaxOff

definelist{MyList}[
  color=magenta,
  pre={This is the text before the list.},
  post={This is the text after the list.},
]{
    item 
        This is the textcolor{red}{first} item of the list. 
        There is some additional text so that it occupies at least two lines.
    item 
        This is the textcolor{red}{second} item of the list. 
        There is some additional text so that it occupies at least two lines.
    item 
        This is the textcolor{blue}{third} item of the list. 
        There is some additional text so that it occupies at least two lines.
    item 
        This is the textcolor{blue}{fourth} item of the list. 
        There is some additional text so that it occupies at least two lines.
    item 
        This is the textcolor{blue}{fifth} item of the list. 
        There is some additional text so that it occupies at least two lines.
}

begin{document}

noindenttextbf{First Two Items:}par
printlist{MyList}

medskip

noindenttextbf{Skipping First Two Items:}par
printlist*[pre,post]{MyList}

medskip

noindenttextbf{First Three Items:}par
printlist[pre]{MyList}[3]

medskip

noindenttextbf{Skipping First Three Items:}par
printlist*[post]{MyList}[3]

end{document}

The options are stored in a property list to be used at print time. The list is split at item which is then inserted back at print time.

Typeset Only First n Items or Items after n from a List

Notes:

Code:

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