Not necessarily. It depends on the changes that you are attempting to do. (The reason that many of them need a regen is because ehteir effects occur at world generation itself. Adding additional reactions is not one of those things IIRC.
Could you post your reaction that you are using please? [code"]["/code] tags around them will be nice.
It is one of those things. Everything is. Every entity is taken from the raws at worldgen, and that entity's raws AT WORLDGEN are going to stay with it.
I hate to say this but, you're wrong. To quote the "when do I need to regenerate" thread:
Most entity changes require a new world.
Most, not all. And permitting reactions is one of those few things that is changeable after world generation. Don't believe me? Go test it yourself like I just did. You can permit reactions just fine for an entity and they will gain access to it. It may (not sure about this) not allow traders to bring the products or invaders come with that metal (such as adding a steel reaction to an entity will), but it
will (sure about this) allow/disallow your dwarves to use it in your current fortress and any future ones that you make in that world.
My guess as to why it wasn't working was one of two things.
1) You modified the overall raws instead of the save ones, resulting in it not being added to your current world.
2) You created the reactions
after the world had been generated. Enabling/disabling reactions for usage is fine after world generation, but adding new reactions is not.
Erm, my pragheels use TURTLE SHELLS to make clumps of organic materials. How can I prevent this? Even though shells and hooves and other such stuff ARE organic materials, I really want the pragheels to use corpses.
Try using [REAGENT:A:1:CORPSE:NONE:NONE:NONE][USE_BODY_COMPONENT] as your reagent. I'm not sure if that will work, but it might.