had this game years ago and after getting back to it im wondering how to mod the game, played enough to want the weight limit changed, also to have a fiddle with whatever i can and tweak some items and settings.
anyone know how?

I only own COP, so I can only speak for that atm, and I at first, I played it vanilla. After that play through, I downloaded and used the Complete Mod for COP, which I downloaded from the 1.0.2.exe link on the page. I just double clicked the exe after downloading, and it self installed automatically with no problems. I actually really liked it, as it improved some broken loot caches and had some very various nice graphic enhancements, including weather effects. Guns names are correct, and look much better as well.

Generally replace the game files, or if editable, text files, like Ini files, direct changes.
<span class="bold">PCGamingWiki PCGW - an encyclopedia of PC game fixes</span>, is always a good source for the basic tweaks, for any game.

The goto site, for most of the best Stalker mods is ModDB, I'd start there.
<span class="bold">Mods - S.T.A.L.K.E.R. Shadow of Chernobyl - Mod DB</span>

Nexus Mods is a late comer to stalker, but has built up a sizable number
<span class="bold">S.T.A.L.K.E.R.: Shadow of Chernobyl</span> 1,021 files

Even starting a section for the full overhaul, and ModDB, Mod of the Year (Beat Enderal to win it)
<span class="bold">S.T.A.L.K.E.R.: Call of Chernobyl</span> 13 files

Each mod will give details of what to do, for that mod, as it can be different depending on the changes done.
Even where the mods go can vary, and no one answer fits all cases.