I think it might be useful to have a USES=replace, similar to USES=shebangfix.
This would replace direct usage of REINPLACE_CMD in ports for replacing %%PREFIX%% and %%LOCALBASE%% in patched files. Patch files would still be required to put the %%PREFIX%% and/or %%LOCALBASE%% into the source(s).
There seems to be a lot of that type of usage in ports right now so I think it would be useful. We could then start separating that type of use of REINPLACE_CMD from other usage and encouraging people to use a patch and USES=replace.
This patch includes a sample port update for graphics/acidwarp-sdl.