it can be done on a standard frame i think, but you will need to drill a couple of holes and tap them to put adjuster screws in, not major work but if you arnt confident to do it best to get somone who is to have a look
that would just soften the pull, i'm a big advocate of jamming stuff in, you could always stuff a rod down the spring to act as a back trigger stop, i dont know if this works as i've never tried it but it looks good on paper!!