I think you may have answered your own question with your topic title.
Try splitting the wall with the Split tool (icon looks like a little red axe) so you can isolate the portions that you want to modify.
This won't effect the existing doors and windows.
It will still be a polywall but it will at least be in manageble chunks.
But once a wall is a polywall then it has to stay a polywall as far as I know.
You can't convert back to a standard composite wall that I am aware of.
You can only go from a composite to a polywall (not back the other way).
Don't forget you can also use the eyedropper to aquire all the properties of a door or window and then place that door/window into a new wall so at least you don't have to figure out all the settings.
The moral of the story is don't use polywalls for regular walls unless you really really have to.
I have never used one yet!
Barry.
One of the forum moderators.
Versions 6.5 to 27
i7-10700 @ 2.9Ghz, 32GB ram, GeForce RTX 2060 (6GB), Windows 10
Lenovo Thinkpad - i7-1270P 2.20 GHz, 32GB RAM, Nvidia T550, Windows 11