I would not top off usually. But when on a road trip across Utah or Montana - that couple gallons may decide whether you would make it to the next pit stop or not.
Charcoal canister is just a tin box packed with absorbent, you cannot do it much harm by overfilling your tank occasionally. But there is a lot of valves and hoses going in and out. Constantly drenching them in gasoline would eventually cause them to fail.
The dealer of course would not try to find the cause - just replace the whole assembly.
Here is an interesting read on the topic:
http://steampunkworkshop.com/toyota-...s-valve-repair

 

I’m currently tip toeing around this same situation. Range hit 0kms about 15kms ago. Im trying to get 15 kms more wish me luck. Based on the 2 gals I should have 7+ litres so at 9L/100km I should be able to get 70kms for sure.

on a side note, I always top off my car to the brim. I have never had any issues except for one car. A 2006 Sienna with 350,000kms throwing the evap code. Which I don’t think was because of topping up fuel but could be.

Top up or not, it’s up to you. Like the manual recommends 5W-30 I run 0W-20. Your car run it how you want it.