Depends on the object. If it has a mesh (GMDC) and texture (TXTR/TXMT), those can be swapped for a different set of mesh/texture.
If it's based on an EAxis item and borrows all the resources from it (no GMDC/TXTR in the file), then it should be possible to change which object it's referenced to.
Also matters if you just want to swap it out as a replacement (simplest option, fine if you just need one version), or want a version that can be used alongside the original (you'll need to know how to clone objects, change the GUID, etc.)
Would help to know which object it is and what you're planning to do. There's a lot of modded bushes, and the functions and setup of that modded bush could depend on what you would need to do to keep them in the object you want to turn it into.