So if one "accidentally" activates the approach, is there anyway to "un-activate" it?
Yes there is.
Reminds me of the time the MCDU temporarily seized up in CRZ at FL390 as I was making a position report. I was new and hadn't seen it do that before. I randomly pressed a few buttons and nothing. Reaching for the books, it suddenly sprang back to life - and remembered the sequence of each button I had pressed...