use of => symbol

In a regular text, I'd simply take it to mean changes/changed into, just like any random arrow, without any sense of desirability. Your particular interpretation is unfamiliar to me, and I believe it is not generally so used. Practice may be different in specific fields.

Of course you could indicate a desirable change with it, but I don't believe this desirability is inherent in the symbol.

As Unreason says, it means implication in formal logic: p => q means "if p, then q", just as p <=> q means "if p, then q; and if q, then p".

In logic it is used for implication, as shown in the table of symbols given by Wikipedia:

• p implies q is denoted with p ⇒ q

This is the 'demands' sense of 'implies', not the 'suggests'. If statement p is true, it necessarily follows that statement q is also true.

The usage is familiar to me also, but I don't know accepted it is. I don't know the approved editorial marks for paper proofreading (proofreading marks, but I've used '=>' in electronic text to say what I think should be done.

Which is to say, it is a reasonable symbol to mean "should be changed to", but therer is no official support for it that I know of.

('=>' has a technical but unrelated meaning in mathematical logic for a very specific kind of implication)

Are you sure it is not → [->] rather than ⇒ [=>]? The first one usually mean to substitute in place of the other.