How to do custom ordering with Datatool

So I have some data for a rock climbing guide I’m writing. In the last page I want to list all the routes, sorted by grade. The thing is that the conventional sorting doesn’t apply here.

Quick explanation of climbing grades (YDS system):

A grade is a one-dimensional quantity to indicate the difficulty of a rock climb. The grades are indicated by numbers, and from grade 10 onwards, are subdivided in four grades, indicated by letters a, b, c, and d.

Examples: 8, 9, 10a, 10c, 11b

Sometimes grades are divided in two, not in four, indicated by – and + signs.
This way, a route graded 10+ could be a 10c or 10d, and in the table it should be displayed between those grades.

So I want to be able to sort this somehow.

MWE:

documentclass[12pt,a4paper]{article}

usepackage{datatool}
usepackage{filecontents}

usepackage{longtable}

begin{filecontents*}{datos.csv}
Route,Grade
Cempasúchil,9
La Gripe, 8
Dopamina infinita, 10b
Casiopea, 11c
El Hombre Avispa, 11b
Tiranosaurio Tex, 11-
Euro Dance, 11a
El Primer Contacto, 12d
end{filecontents*}

pagestyle{empty}

DTLloaddb[keys={Route,Grade}]{datos}{datos.csv}
DTLsort{Grade=ascending}{datos}

begin{document}

{tiny
noindent
begin{longtable}{ll}

  bfseries Route & bfseries Grade 

  DTLforeach{datos}{%
    pname=Route,pGrade=Grade}{%
    pname & pGrade 
  }

end{longtable}
}
end{document}

Output:

Correct order:

8, 9, 10b, 11a, 11-, 11b, 11c, 12d

Solution ideas:

-Split the number and the letter, and sort by two columns. I like this solution, however, it would probably put + and – grades at the end of that number (I could live with his). Also I would like to do this splitting in datatool, not from the source.

-Maybe there is some way to specify custom order. I would not mind having to type all the possible grades by hand, there aren´t that many (hardest route in the world is 15d, but for the guide they range from 8 to 14a) To solve this maybe modifying or creating a custom handler (like dtlicompare)?

Char  ----> New Code
8     ----> 1     (8 always goes first)
9     ----> 2     (9 always goes second)
a     ----> 96    (move the a back one code, to put - between a and b)
-     ----> 97    (right between a and b)
+     ----> 100   (Right after the c)
d     ----> 101   (d is displaced by the d)

renewcommand*{dtlsetcharcode}[2]{%
  ifstrequal{#1}{8}%
  {%
    #2=1relax
  }%
  {%
    ifstrequal{#1}{9}%
    {%
      #2=2relax
    }%
    {%
      ifstrequal{#1}{a}%
      {%
        #2=96relax
      }%
      {%
        ifstrequal{#1}{-}%
        {%
          #2=97relax
        }%
        {%
          ifstrequal{#1}{+}%
          {%
            #2=100relax
          }%
          {%
            ifstrequal{#1}{d}%
            {%
              #2=101relax
            }%
            {%
              #2=`#1relax
            }%
          }%
        }%
      }%
    }%
  }%
}