Hey @BenLee, sorry but there’s no thisRow in the context of a canvas button (I just had to check it myself because that’s what I believed but your post made me doubt that).
@Jaisil_Muttakulath_Joy is correct, the proper way to perform the change individually on each row is to use Table.FormulaMap(CurrentValue.ModifyRows(...)). The mass-ModifyRows on multiple rows at once is only possible if you want to set the same value (evaluated once) on all rows, not individually calculated value per row. That’s why there’s no CurrentValue in that context.
And yeah. spamming the undo queue is a known issue. One of the reasons I don’t depend on undo at all, and just prefer to hide that alert altogether. If needed, I’d rather make my own button to “undo” the change.
A somewhat related request: Add an action to show custom alert (dark popup in the bottom)