If I have 5% 100k resistors but wanted 1% precision, can I use 4 of them in series parallel to improve on the 5% precision?
No, the precision remains the same regardless of the configuration. You're stuck with 5%, unless you reorder the correct parts, or you test them with a reliable DMM. I have to say that the last time I tried this, all the resistors in the batch had almost precisely the same resistance though (I can't remember the value, but say it was nominally 1K, they were all 992 ohms or something like that).

If you think about it, it has to be this way. If you could create higher precision from combining lower quality components, you wouldn't need the high precision ones in the first place...