Be aware that while this change does work (just like it does with the Pamac icon), it will revert back to previous state with next update of the application.
The reason is that the /usr/share/applications/ desktop files are part of the application package and will be replaced on updates.
But any .dekstop files that matches them in your own .local/share/applications folder takes priority over the ones in /usr, so that will get used instead, even if the original one gets replaced with an updated one.