That's right, just put in the new file and it should work just fine.
The trick with some files, including spell cast bars, is that they make changes to the EQUI_Animations.xml file. The best way I've found to get around this, tedious as it is, it to open both files in notepad, and look for lines that don't match, ie. different x,y locs, or texture files. Sometimes you have a texture with the new mod that will give you an idea what to look for in this case.
And some poeple with complete sets, such as vert, have fixes so that t.king books and icons work with them, so if you don't feel comfortable messing with the code, you can look for these also.
But as long as the Animations file is not part of the new mod, it should work just fine.
Good luck.
Edit: it doesn't hurt to make a backup of your skin if you do mess with the animations file... just in case.