LoadIconStrip uses pixmaps not images so there should be no theoretical limits.
If there is it needs fixing so pls send me an example png/bmp that breaks LoadIconStrip.
If you want more flexibility you could create the pixmap yourself and then use loadpixmap and pixmap.paste to add / modify individual icons, calling LoadIconStrip(pixmap) and SetGadgetIconStrip after to refresh your gadgets.
If there is it needs fixing so pls send me an example png/bmp that breaks LoadIconStrip.
If you want more flexibility you could create the pixmap yourself and then use loadpixmap and pixmap.paste to add / modify individual icons, calling LoadIconStrip(pixmap) and SetGadgetIconStrip after to refresh your gadgets.