Sorry, I don't get the full picture here.
Does &Prior_Month_End has datetime value?
Is this only used for your title statement?
If it's only for displaying a %substr would do:
TITLE1 "%substr(&beg_date,2,9)";
If you want to use for some subset, I guess you need to get the datepart out of it, here you can use %substr as well (as long as you are sure of the format of the value):
%let beg_date = "%substr(&Prior_Month_End,2,7)"d;
Or nicer, working with a SAS date function:
%let beg_date = %sysfunc(datepart(&a));
Hope this helps,
Linus
Data never sleeps