If I'm understanding correctly, can you simply do a Find/Replace? Ctrl+H enter 1 in the 'Find' and 4 in the 'Replace with' and step through using the 'Find next' button so as not to change any other values in unrelated cells.
When I've done this in the past, it gets awkward when you've changed all the 1's to 4's then when you want to change the old 4's to 1's there are loads, so initially change 1's and 2's to a symbol (E.g. * and ^) then change all the 3's and 4's to 2's and 1's followed by changing all the *'s and ^'s to 3's and 4's.
Look, I know what I mean even if that doesn't make any sense to anyone else :-) lol
If that's gibberish to you, post back and I'll try and make more sense.
If its the values in the cells cant you just hilight all cells you want to change and use Edit > Replace (ctrl+H) Replace all 1 with 5 Replace all 4 with 1 Replace all 2 with 6 Replace all 3 with 2 Replace all 6 with 3 Replace all 5 with 4 Bit clunky ....Or have I misunderstood (quite common)