If you do mess them up, buy replacement screws from mcmaster, but get the oval head philips screws. There is more meat to grab onto, and they are stainless.
90258A221
18-8SS Metric Oval Head Phillip Machine Screw M4 Size, 16mm Length, .7mm PitchIn stock at $8.60 per PackThis product is sold in Packs of 100
And for the needle/seat/lever arm screws:
90258A178
18-8SS Metric Oval Head Phillip Machine Screw M3 Size, 8mm Length, .5mm PitchIn stock at $4.17 per PackThis product is sold in Packs of 100
Yes you get 100 of each, so you can do 50 individual carbs for $13. Not bad. You can have them in less than 2 days with normal shipping.