You can't edit a gameplay tag when you bulk edit via the property matrix.
Found in 4.23.1 CL#10757647
Reproduced in 4.24.1 CL# 107567474.25 Main CL#10868506
1. Create at least two gameplay tags.
2. Create an actor(TestBP) that has a Gameplay Tag variable (GTag) and set it's default value.
3. Right click TestBP and select Asset Actions->Bulk Edit via Property Matrix.
4. Try to alter the value of GTag.
Result: You can't alter GTag.
Expected: You can alter GTag.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-86155 in the post.