Either I gave up searching too early, or I can't believe nobody has even proposed such idea.
Modding a map may sometimes take a lot of time. You know what else takes a lot of time? Applying those mods. You can't really see how the pattern looks like until you have applied the mod. So the basic idea to this feature request is much how text compare or better yet Github's code changes works: Deleted notes are highlighted red and added notes are highlighted green. The modder would just select the highlighted part (or individual edits) and hit the apply button or the reject button. Then the modder can test the map and revert if he/she thinks the mod is no good. It would display the maps much like the reference difficulty option in the file menu, only for all modes. Yes, the 2 maps will two be displayed at a smaller size, but that's not an issue since you are just comparing and testing the mod and not mapping note by note.
Modding a map may sometimes take a lot of time. You know what else takes a lot of time? Applying those mods. You can't really see how the pattern looks like until you have applied the mod. So the basic idea to this feature request is much how text compare or better yet Github's code changes works: Deleted notes are highlighted red and added notes are highlighted green. The modder would just select the highlighted part (or individual edits) and hit the apply button or the reject button. Then the modder can test the map and revert if he/she thinks the mod is no good. It would display the maps much like the reference difficulty option in the file menu, only for all modes. Yes, the 2 maps will two be displayed at a smaller size, but that's not an issue since you are just comparing and testing the mod and not mapping note by note.