I have to replace values in some cells without changing the values of other

Hello, I'm having trouble replacing values. I have a lot of columns with values arranged like this :

50 - 5 - 49 - 4 - 50 - 46 - 49 - 46 - 5 - 46 - 4 - 46 (just an example, values are different on other columns, but it's the same problem)

I need to replace all cells the contain only "5" into "45", and "4" into "44", but without changing the cells containing "50", "49" or "46". Each time I tried to replace, the "50" turned into "450" etc.

Is there a way to ignore the cells I don't want to change ? I really don't want to do it manually so If someone has the solution, it'd be greatly appreciated...

EDIT : I think excel just trolled me, because I clicked on "whole cell" earlier and it didn't work, made the post, and now it works... Sorry to have wasted your time everyone...