Before, I was bending like crazy. 10's on a strat, bending up to a diminished fifth on the G, a major third on the B, and a minor third on the high E. I modified my intonation a little. However, just a week after, I snapped the high E string while doing one of my usual solos with a full bend / excessive vibrato at the 20th fret.

My strings were old so I assumed that it snapped because of time. However after two weeks after changing strings, I could not bend easily anymore while in standard tuning (E string). I'm not sure if this is a physical or psychological issue, but I can barely bend the 22th fret on the E string. Sure, around the 15th fret it's fine (I can tell, it's a lot harder now), but anything above the 19th fret and it's hard. Also, when I bend excessively, sometimes I hear a small creaking noise coming from the headstock (this actually happened before I broke my string).

Any tips? I don't want to go to 9's, that would be really bad. Does modifying intonation affect the playability? I was going to modify my action but at the moment the E string is already lower than the others.

Try putting some graphite on your nut. The string may be pretty tight in the slots, so that may cause the creaking. It wouldn't make it harder though. All I can say for that is just keep bending until you get used to it, and have extra strings on hand.
This may seem obvious but you could try stretching the string a bit, like you would just after replacing it.
E string's usually first to go. I change strings economically enough that I break them(Pink Floyd Solos are terrible for this).

Few things :
Be sure you did change to the same guage of strings.
The Strings were old and well worked in. It may be just that you have to let them stretch and slacken a bit. Be sure to stretch the strings during restrining.
lastly: Examine the nut, it could be worn and causing problems. Using graphite like the guy said is a good fix.
Also to fix a nut you can superglue and file a new one.
On playing the Paul Gilbert signature at the guitar store extensively, my missus sighed:
"Put it down now, It's like you love that guitar more than me!"
In Which I replied.
"Well it has got two F-Holes!"