Unless I'm missing something, replacement and substitutes are already synonyms of substitutions - see its synonyms page. If for example you type replacement in the tag field, substitutions will show up instead (with an "also: replacement" below) and you'll end up with the right tag.
I started to implement your suggestion, but had to stop in the middle of doing it.
What tripped me up was this question.
Pickling green peaches: is the fuzz a must?
I recognize your good intentions, but English turns out to be more complicated than that. Nobody says "peach peel". People won't search for that. If I write into the tag wiki for skin to only ...
"Will dry ice be too cold for my fesh, unfrozen steak?"
"Do fresh vegetables belong in a meat freezer?"
"Do those bowls of ice really keep milk cold enough?"
"I've been fishing for days, and finally caught the big one. It will take me all day to sail back to Santiago. Should I keep it in the nice cool water, or haul it up on the predator-free deck?"