That's done via a simple switch. I'll just put this in psuedocode. (Not real code, you can figure out what goes where though).

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Page 1:

<>Choice: "Bribe Guard with 500 Gold"/"Cancel"
...<>"Bribe Guard" choice:
......<>Branch: Check if Gold > 500
.........<>Deduct 500 Gold
.........<>Move Event: left, left, face down
.........<>Set Switch: [xxxx:BribedGuard]
.........<>
......:Else
.........<>Message: "You don't have enough!"
.........<>
......:End
...<>"Cancel" Choice:
......<>
...:End
<>

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Page 2:
Precondition: Switch [xxxx:BribedGuard] is ON

<>Message: "Hi"
<>Move Guard left, left, face down (ignore impossible movement, it's a checkbox below the list of moves)
<>