Addition Subtraction - Aedif/multi-token-edit GitHub Wiki
Numerical fields can be added and subtracted instead of overriding the current value. This can be done by right-clicking the numerical controls in the Mass Edit forms. ${\textsf{\color{green}Green}}$ background indicating addition, and ${\textsf{\color{red}red}}$ subtraction.
Text fields will instead append or remove the entered text from all selected placeables. By default appending will be done to the end of the string, but this can be changed by adding >> to the start of the field.