It's now possible to change the shortcut that enables planar transformation with the transform manipulators (shift+LMB on axis).
This actually fixes the workaround added in rB20681f49801fd. Thing is that we needed to allow using the manipulators, even if a modifier key is held so things like snapping work right away. That's why normal LMB behavior uses KM_ANY. However, event handling would always execute the KM_ANY keymap handler because it's iterated over first. Simply solved this by registering the KM_SHIFT keymap item first, so it has priority over the KM_ANY one.
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