I should maybe of made myself clearer from the outset as to the purpose, but I thought it best not to interfere with the process that is the forum-mind.
My reasoning for asking the question is a simple one, but I realised that it would have a broader audience if I left it as was for the time being. I have an old 1960s 'plastic' (I think) bow. It is 32# @ 27". I'm not sure as to it's history but want to use it as a tool for measuring draw length. At the moment, drawn to my draw length it is pulling goodness only knows what poundage. I just wanted to drop the poundage to make it a lighter bow for measuring purposes. I knew there would be issues around 'just adjusting the bowstring length' hence me not explaining initially.
Cheers Si2 and Greygoose.