libgweather uses a patch system, which allows changes like this to persist between package updates. https://wiki.ubuntu.com/PackagingGuide/PatchSystems explains how to use this, pretty much you check whether the package uses a patchsystem with "which-patch", and in this case, use "cdbs-edit patch PATCH_NAME", make your changes, exit the new shell it provided you, and then make your debdiff.
Please also consider pushing this patch upstream.
@Ted:
libgweather uses a patch system, which allows changes like this to persist between package updates. https:/ /wiki.ubuntu. com/PackagingGu ide/PatchSystem s explains how to use this, pretty much you check whether the package uses a patchsystem with "which-patch", and in this case, use "cdbs-edit patch PATCH_NAME", make your changes, exit the new shell it provided you, and then make your debdiff.