A simple modification, so :
Find this line
(setq sel (entsel "\nSelect Line : "))
And change it to this
(setq sel (entsel (strcat "\nSelect Line " (itoa snum) " : ")))
Pretty sure this should do what you want, but I can't test as I only have a LT version with me at the moment. If it doesn't work let me know and I can sort tomorrow.
if you need to do the same for the text (when applicable)
Change
(setq sel (entsel "\nSelect Line Text : "))
;TO
(setq sel (entsel (strcat "\nSelect Line " (itoa snum) " Text : ")))