Is there a formula for Find & Replace? Specifically for replacing numbers with other numbers?

I have a document with 11 pages of various number combinations that look a bit like this:

A-1, 6, 7, 8
A-3, 8, 1, 2
A-5, 2, 3, 4
A-7, 4, 5, 6

I need to change all the instances of...
"1" to "8"
"2" to "1"
"3" to "2"
"4" to "3"
And so on...

I would do a simple Find & Replace, but by the time I get to the final one (which is changing "8" to "7") the Find function will locate all the "8" including the ones which used to be "1". Get me?

So if there were a function or formula that could just subtract 1 from the value I'd be set.