Bubbler overflow 1st ferment

You did the right things. I typically sanitize my blowoff tube but I'm not sure it will cause any damage...

 

Also, I use a StarSan solution as my blow-off liquid instead of plain water. That way, there's no chance of infection if there is suck-back.

Just make sure you don't cool the fermenter with that rig attached or your water will likely travel through that unsanitized tube and end up in your beer. You'll see the krausen drop soon. At that point, you can reattach the airlock if you wish.

 

I always start fermentation with a blow off, and I just used distilled water. The only time you have to worry about suck back is if you cold crash. Once fermentation dies own I use a 3 piece airlock with sanitizer since that is what I"ll cold crash in.

 

That's not entirely true. You can also get suck back if you pitch high and lower to fermentation temperatures after you've sealed the fermenter. This isn't really an issue though unless your blowoff tube is really short. This is more relevant when it comes to airlocks.

I always start with a blow off as well, unless I have tons of headspace, which is rarely the case. I wouldn't cold crash with a 3 piece airlock, though. Those will allow your sanitizer solution into the beer, and air in after the level of that gets low. At least the S type airlocks don't let liquid it.

 

So.... when you lower the temp.... like when you cold crash.

Just lowering the temp a few degrees will not have a significant effect if you are lowering while fermentation is going on like you say you do. This is because CO2 is still being expelled by the yeast.

It's kind of odd though because most experienced brewers either maintain one target temp during fermentation, or prefer starting low, and increasing temp over the course of fermentation, before cold crashing post fermentation if they elect to cold crash at all. Why would you decrease temp during fermentation? That seems counter productive.

 

I was referring to lowering the temperature of the wort after pitching, but before fermentation begins. I don't think you would ever actively work to achieve that scenario, but it definitely happens. You chill your wort to "pitching temp" which I think a lot of people ballpark for various reasons (e.g., warm summer tap water, impatience, etc.). Then you throw the fermenter into your fermentation chamber, whether that's a temp controlled fridge, freezer, bucket of ice water, swamp cooler, basement, etc. If you figure 75° is good enough for pitching, then move it to your 65° (because, say, that's within the ideal range for your yeast) basement, you're likely to get some negative pressure as the temperatures equalize over the first several hours, because the yeast are likely not active yet (maybe unless you pitched a big starter at high krausen). With some dry yeasts, a lag phase of up to 48 hours isn't unheard of, so the window of opportunity for this type of thing to happen could be sizable.

Probably not the best practice, but it's worth being aware of in case it happens. I've definitely had a little StarSan end up in my beer that way when using a 3-piece airlock.

 

If you are chilling in a fridge /cold room, then pitching yeast, I suggest not using an airlock until you pitch yeast. Just throw some sanitized foil on top. Even if you didn't, a difference of temp by 10 degrees is insignificant as far as the gas density as a product of temp is concerned. In the end, it really doesn't matter and it's not worth a second thought. Even if you did wait 2 days, the yeast will take care of your gas problems

 

I kinda doubt you'll risk much. And most of the information being provided here is way more advanced than what you need to get your head involved with on your first batch.
Some of the knowledge being dispensed above is great, for future use, and when you get a few more batches in you and get comfortable with some of the yeasts you will probably end up preferring.
You're probably not using any form of temp control, so the temp swings are probably going to be within the 5ºf above ambient that yeast typically works at when you free ball your fermentation. As it's your first batch. You're probably following every rule to the letter and pitched at the appropriate temp. Good. You'll eventually figure out what to tweak, and there is plenty to tweak.

Your actual post.
NBD on what you're worried about. If you want to make it a big deal. If the beer needs dry hopping. Do that, and swap out the blow off tube for an airlock with sani in it when fermentation has started to subside, and then ignore it until its time to bottle.
Don't get involved with pitching high, or pitching low until you get comfortable with the yeast you are working with, and how they will perform at the temp being recommended you pitch them in at.