I was thinking, bad idea I know, of letting the players "keep" the Luminous Reproach "for now" if they do well on Shades on Twilight.

Knowing that the most likely character to wield it would be the psyker (the rest are dakka dakka boys). Could I re-write it to be a force weapon as well without overpowering it?

I didnt know it wasnt a force sword, our GM let me use it as a force sword but there was no fancy stats on it, atleast as far as I was aware. But we didnt get to keep it afterwards anyways.

The sword is a revered artifact of the Inquisition. It is highly unlikely that the Inquisition would let such an artifact be kept by lowly Acolytes. However in the end it is your campaign.

As written, it's a power weapon. The fluff does allow for force weapons with a power field, but strictly speaking I don't think the RAW of Dark Heresy does. I suppose it would be possible, but following the precedent set in the errata he couldn't use the Force abilities unless the power field was switched off. Personally, I'd say a force power sword would be overpowered, but if you replaced the powerfield with the Force circuitry and stuff, that might be fair. Then again, it is a relic weapon, so...

I'd also note that I personally wouldn't let them keep such a holy artefact weapon, especially one thrice blessed by the hand of Thor. I might let the psyker get his force sword blessed, but not by anyone so important. Essentially- holy force sword=nasty. Holy force sword with extra rules gubbins (and maybe a power field)=way too powerful to let them keep

Thanks for the advice. I will say my intention was never to give it to them permemently. I would let them have "a play" with it and then take it away as it was needed elseware.

My finance's Scum, Narla, weilded Luminous Reproach for one episode. We had to Scotchgard the blade to keep her drool off of it. Next up is Tattered Fates , so the blade is lost to the group for the time being... I'm not sure when the blade will return, but based on our Psyker's love for Force Weapons, Grimm will not have it as a force blade.... too much dakka already.