I think cutting off some portion of the pesi would be alright though I've heard that the isi is actually staying at the base of the pesi. An old wiseman once told me that if tha khadam can stay in the keris (with the sheath on) for 5 minutes, it is already very good, for it normally comes to the keris when the keris is unsheath (some sort of calling the khadam to come).
I have an old raja gundala pamored keris, that recently was used successfully to exorcised my late former mother in law old house. The thing with that keris is, the pesi was accidently broken about 1 inch when I tried to take off the hulu. Initially I thought my action had rendered the keris useless - but my quick thinking to restore it (without soldering the pesi) by permanently gluing the shortened pesi to the handle, the keris DID NOT lose its power nor its aesthetic outlook
