modifying a 250K ohm pot into a "full pass" pot ?

How would you go about doing that?

What IS a full pass pot?

wiki and google are silent

The tech I was talking to described it pretty much as a pot that is totally bypassed when turned down to zero.

Think that is more commonly known as a 'no-load' pot as the load is removed at the end of the rotation.
you could disassemble it and cut the track at the lowest point of rotation
or if it has an opening, you could use nailpolish to cover that part of the track.

Remember, that only works for a TONE pot - NOT a volume...

Every day's a school day

AND, you want the "null spot" at the "10" end of the tone pot's sweep, not the "0" end...

http://www.tdpri.com/forum/tele-technical/127070-no-load-mod-cts-pot.html

Thanks that thread link is incredibly helpful

Yes, Rob has already shown us an easy way to do this. make note if it - it works, trust me. Well, okay don't trust me, just try it yourself.

A no-load, or full-pass pot is the secret to the "Delta tone" feature of many Fender models. when the tone pot is turned up all the way, it's as if there's no tone control at all on there - just like the bridge pickup on a vintage-wired strat.