(Update) code at the top of this post does NOT work

perl -pi.bak -e 's/(?<=weak<INPUT TYPE=radio NAME=(\w{2}\d\w{2}) VALUE
+=\d>(?:<INPUT TYPE=radio NAME=\1VALUE=\d>){6})(?=strong)/insert($1)/e
+ig;
BEGIN { sub insert { my $name = shift; return "value 8, value 9, value
+ 10"; } }' *.html
[download]

Explenation of regex:

  s/
    (?<=                  # Look back-group
     weak                # Match the word weak
     <INPUT TYPE=radio NAME=     # tag
     (                   # Capuring group: $1 / \1
       \w{2}\d\w{2}      # 
     )                   # End-capture
     VALUE=\d>           # tag
 
     (?:                 # Non capturing group
       <INPUT TYPE=radio NAME=     # tag
       \1                # It's possible that this should be $1, as I 
+said, the code is untested.
       VALUE=\d>
     ){6}                # There are 7 input tags, one already matches
+, so 6 to go.
     )                   # End look-back
     (?=                 # Look-ahead-group
       strong
     )                   # End look-ahead
   /
     the text you want to insert
   /ixg;
[download]

Big note, the code in the explenation will not work properly, because the x-modifier is in use and I did not escape the whitespace!

Update: after reading the reply of Anonymous Monk, I decided to test it... the variable lookbehind error comes from \1. This can be fixed by using (?=\1).{5} instead of \1, but then another errors shows up: 'Lookbehind longer than 255 not implemented'. This makes it impossible to use a look-behind...

So there is only one thing left to do and that is making it a 'real' group of it...

Then the short (and tested (or atleast on simple data)) version would become:
perl -pi.bak -e 's/(weak<INPUT TYPE=radio NAME=(\w{5}) VALUE=\d>(?:<INPUT TYPE=radio NAME=\2 VALUE=\d>){6})(?=strong)/$1 . insert($2)/eig; BEGIN { sub insert { my $name = shift; return "value 8, value 9, value 10"; } }' *.html

The differences:

• A capturing group is used,
• $1 and \1 changed into $2 and \2,
• $1 . insert($2),
• The input pattern is corrected (I used \d where it should have been 'v')
• A space is added between \2 and value (it was missing)