Is there a way to "specifically tell" any given spell/effect to refresh itself instead of stack the effects?
For example, some effects are never cumulative and always refreshed yes? Like haste or stoneskin. AFAIK if a source sets 200 stoneskins but 1 second later a different source sets only 1, the creature loses 199 stoneskins. Same for the duration of a haste spell.
Then there are effects that use the same opcode but allow multiple instances, like +/- values to hit or AC or etc.
I'm trying to apply spell/effect that should refresh itself based on conditions that may happen at random, so whenever the condition activates, the spell/effect needs to either recognize that the creature is already under its effects and just refresh durations, OR remove the previous instances and re-apply anew. The problem with removing/re-applying is that it doesn't seem to happen accurately, sometimes it takes a while and sometimes it will just remove everything, including the new instances.
The bard song seems to use a combination of
Removal: Effects specified by Resource 
Protection: Immunity Spell 
at the top of its own effects list, and both tartget itself in the resource field, while it does (strangely?) work for the bard songs, it doesn't seem to work for other things that I tried.
Does someone has comments or guidance/advice in this? Thanks very much btw!