I suggest creatinga new pad stack just in case any other symbol in your library uses the padstack that you want to edit.
Allegro has several options to refresh the pad stacks, of which some will refresh ALL pad stacks in the design. This can be a fatal mistake!
(Some designers creats different padstacks with same name residing in different library trees. One tree for reflow soldering, another for solder wave etc. Then it is possible to have multiple choises for same symbol depending on soldering method. The paths to the padstacks can then be set in the user preference menus)
First you open the symbol in Allegro editor. Then you use the tools menu in Allegro to find padstack sub menu. You will there be given the option to change and/or refresh the symbol pad stacks.
If you create new padstacks with different names you can change them selectively one by one or all at one time.
(I do not have access to Allegrio right now but I have done this myself)