i would like to give two different situations and imagine your are the end user of your site.
1)(Allowing perl to add new fields as per your thinking) would you like if your sites page checks with server each time you change a value and take more than a minute to load
2)(using client side script like JS/Ajax)
would you like to get your site loading changes faster in less than seconds when ever you change the value
which site will you take as an end user??
i will choose second one
then you should program it such a way that it benefits the end user.
NB:"i am not jocking at PERL"