Can you use a Pass INT 250 as an amp (bypass its pre amp)?

Oops,
dpac996 is correct and after I read the manual it confirms there is no dedicated main preamp inputs.
it’s been 5 yrs since I owned one of these,with lots of different gear in between.I currently have a new Modwright and it definitely has them with a HT bypass.For now I’m just using it as Intergrated but I’m sure over time I will experiment.

No there is no “main in”
You would simply treat your external preamp as any other source to the 4 inputs; set the volume control on the pass to about 55 and use your other pre;
the internal line stage in the Pass is very transparent and will let the character of whatever preamp you use to shine through; 

you can use the PREAMP OUTPUT  to drive another amp or sub 

I have this Int 250 and really like it.

You have to spend double for separates of equal power to improve; good luck

Yes,has preamp inputs.One set of rca single ended and one set Xlr balanced.
I use to own one of these Intergrated amps and it works great with another preamp of your choice.