If you wanted to replace that monster of a formula for the description with something a little more bearable, with the desired text change, collapse the sheet and try this one instead (in cell C16, I suspect):

=GLDESC("Accounts Receivable",3,$B16)

This description field will print the text 'Accounts Receivable' when the sheet is collapsed, the actual account description when expanded, and prefix whichever text by 3 spaces.

Your change above should have worked, provided that cell A16 actually contains the text '.Range'.
If you don't intend to allow breaking out each A/R account on separate rows (ie you always want the sum of the 4 accounts and never each one) and have deleted the .Range text, then forget the whole formula stuff and simply overwrite everything with the straight text 'Accounts Receivable'.