>perl -wMstrict -le
"printf qq{'%s' yields '%s' \n}, $_,
   join '',
   map   /\d/ ? qq{arg$_} : $_,
   split /(\d+)/
   for @ARGV
   ;
"
"1:2"  "-p 1 -t 2 3"  "1 2"  "12"  "no digits"
'1:2' yields 'arg1:arg2'
'-p 1 -t 2 3' yields '-p arg1 -t arg2 arg3'
'1 2' yields 'arg1 arg2'
'12' yields 'arg12'
'no digits' yields 'no digits'
[download]

Note that  split /(\d+)/ does not give the OPer's specified 'arg1arg2' from '12', for which  split /(\d)/ vice  split /(\d+)/. (However, I still prefer the  s///g approach.)