Fix issue with D274/rP22767 - modifications are a list of effects, not a single effect

D274 introduced a silent change that modifications would only have one effect per value-path, which was an unnoticed regression.

Detected following the comments from SonarQube reported here: https://code.wildfiregames.com/rP22767#inline-4214

Comments By: elexis

Differential Revision: https://code.wildfiregames.com/D2315