# Variable subscript substitution - easy way?

I have a Mathematica expression with about 900 terms, that looks roughly like this:

$$X_{1,1} + Y_{1,2} + Z_{1,3} + XX_{1,4} + XY_{1,5} + ...$$

Is it possible to perform a fast method to copy this expression with just the first subscript changed to all 2's instead of all 1's as in the first expression? I.e.,:

$$X_{2,1} + Y_{2,2} + Z_{2,3} + XX_{2,4} + XY_{2,5} + ...$$

Thank you.

• You can use replacement rule like Subscript[a_, 1, b_] -> Subscript[a, 2, b] – roman465 Oct 21 '19 at 0:20