I think the problem of GIMP not being able to open png files has nothing to do with the changes you made.If I enable the GIMP plugin, it will be built and is under stage, but it is not installed. And it's not in pkg-plist and not added.
I rebuilt gimp-app, now gimp can't open png files any more ("the plugin crashed")!
This should be a bug report for "exiv2" not graphics/gimp. Downgrade "exiv2' and it works.I think the problem of GIMP not being able to open png files has nothing to do with the changes you made.
See: graphics/gimp 2.10.8: “gimp_wire_read(): error” when opening file
It seems there's a general problem with GIMP plugins not loading as they should, caused by an exiv2 update.
Hope it gets fixed soon
This should be a bug report for "exiv2" not graphics/gimp. Downgrade "exiv2' and it works.