I've been tweaking my jetting since I got this bike. I keep going leaner and leaner as it seems to run better. I'm at 162 MJ and needle position #1. All else is stock. I read every post on jetting and have never heard of anyone being that low. I felt comfortable with that setting riding at 6000-10000 ft but with winter coming I'll be riding more at 4000 ft.

I just put on a ZipTy fuel screw. My 'factory set' position was 3 1/2 turns out which is rich as I understand it.

Should I go richer on the main jet and needle position and turn the fuel screw in to lean it up? The instructions with the fuel screw say if more than 2 1/2 turns out go bigger on the pilot jet but the extra pilot jet that came with the bike is smaller.

I've tried to download the jetting spreadsheet from Thumperfaq but I don't have Excel so it won't work for me.

Any suggestions will be appreciated. My bike runs pretty good but I don't want to blow it up.

at your elevation, probably not.
generally, you can go mega lean and not hurt anything.
i know what my bike does on an Exhaust Gas Analyzer and it is quite shocking just how low you can go.
btw, the leaner you go, the more overrev hp you make (to a degree).
in my dyno tests, i gained 1.1hp (past peak) by going 4 sizes smaller on the main and i never went under 5.3% CO!
the fuel you run can also make a BIG difference.

Go leaner go meaner....I run in the mid 150's on my WR400. I run from 4500 to 14000....and don't change my jetting when I go to Moab.

a wr400f and a wr250f can NOT be compared in any way, shape or form.  jetting or otherwise.