Yeah, I know they're less likely, but I'm just trying to get my new, non-expired stickers on the car

My parents are getting kinda tired of driving me into work for 10pm and picking me up in the morning when I'm done.
After I finally got some premium in the car, I drove it a little hard, to see what it's like and all. I let off around 90 or so, and when I got back down to around 60, I noticed the damn CEL was on. I pulled into a grocery store parking lot, and checked the codes. I actually got the oxygen sensor code. I cleared the codes and it hasn't come back since. Believe me, it is near the top of the to-do list for the car, after getting my stickers. I want it to run like it should. I did kinda have to replace that knock sensor though, the old one was cracked.
Now, I hate to sound like an idiot, but with the PCV valve, could I leave the actual valve in there, but attach a hose to that? And, is SeaFoam available at normal auto parts stores? I didn't have a chance to run in to Autozone this morning like I wanted to.
The idiots at Walmart only put in 4 quarts, and I just checked one of my '91 manuals, and it says 4.8, so I had to run back in and buy an extra quart. I noticed when they first started it to pull it out of their shop, it was ticking real freakin loud, and it continued to do it for about 20 minutes afterward. By the time I got home after scheduling a retest, it ran fine. I noticed that after the oil change, it pulled even harder than after I did the plugs and wires.
When I did the plugs, I didn't remove anything really. There was those two hoses that really restricted access to that plug, and I pulled one off for about 20 minutes or so. Just before I finally got that damn socket to release, I was thinking of removing the bottle. I was trying to keep things somewhat simple like that, if it makes any sense.
Yeah, I do plan on getting everything with the car working properly in time. I'm not just gonna get the waiver (if I have to), and say "oh, it's fine now." or anything like that. I'm kinda rescuing the car from the damn ricer 20 year old kid who owned it before me. (granted I am 20 also, but I actually respect the car, and I know what it is)