I’m knitting a christmas stocking and I knit a row which should have been a decrease row. Needless to say, I didn’t make the required decreases at the end of the rows. Can I make the decreases on the next row which is a purl row? I’m trying to avoid taking the row out. Will it make much of a difference?
Yes, go ahead and dec on the next row, just do the next decs on the correct row instead of counting from the row where you actually did the decs.
I don’t see why not if you’re working in the same color. One extra row probably won’t make any difference to the look of the stocking. 
If you are doing color work on those rows it may change something so keep that in mind.