In the properties dialog for a symbol, the Image Tab has a drop-down to select another image. The drop-down lists 15 possible replacements. But it seems to offer images of the same file-type; not from the same Palette.
In the two screenshots below, the icon used to create the symbol was: in the first an SVG, in the second a PNG.
⇔SVG | PNG⇔
Requests: (for when this bug is addressed)
The offered images be from the same Palette as the original / current Palette.
The list be scrollable.
A button be added to view the symbols from another Palette.