I'd say the opposite - in your shoes, I'd just try it, doomed or not! (But then again building an IDE is My Thing atm - check my profile.) Building one of these systems is going to be really fun.
If you don't have the time/inclination to just do it cause it's a cool project, one option is to "paper prototype" the feasibility of the transforms you'd need.
Next time you're writing any code in the first language you want to support in that AST editor, take a screen recording of at least half an hour's coding. Watch it back later, and keep a count of how many times you:
* transition from one valid program to another in a simple way (eg just writing a line of code from scratch that's valid first time)
* transition in a way that would require abandoning your keyboard and reaching for your mouse in your editor (NB this is a seriously slow operation, usually taking a couple of seconds or more).
* transition in a complex way your editor would support if it had that kind of transform built in (eg if/else-> switch), and work out exactly how clever that transform would have to be (would it work if the if/elses weren't simple equality checks? If they weren't, how would you make the transform if you weren't allowed any non-compiling code?) Then enumerate the distinct such transforms you'd need to cover that half-hour of typing. (You will probably discover a Pareto-type distribution - the question is how tight the head/long the tail is. My guess is you'd need a huge number of special transforms to cover 95% of your edits, but data beats guessing)
* Jump around between statements (eg half-write something, leave it in an utterly broken state, then go actually define the variable/function you're using, then jump back and finish your thought). Your editor would have to permit this somehow or it will be really frustrating to use.