In reply to:

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y=z // visual to visualseek
x=y // custom button to visual hex code

one would expect that hijack would see the relationship, and would automatically do x=z

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No, because that would stop you (for example) swapping two buttons on a standard remote, or doing this one of mine:

;; Increase stalk volume control speed
KVolUp=VolUp,VolUp,VolUp,VolUp
KVolDown=VolDown,VolDown,VolDown,VolDown

(well, it would if I'd used KVol{Up,Down} on the RHS, anyway).