Yes, you can, but the whole point of it being random is that it is otherwise much easier to guess and much less secure.
If you select a “user friendly” pass phrase, how likely is it that another person will select a pass phrase that shares 9 or 10 words with your pass phrase?
It’s a very bad idea for security, but Counterwallet will not prevent you to use any 12-word pass phrase from the 1600+ word list.
Remember that Counterwallet has no 2FA or additional password - precisely because the randomly selected 12 word pass phrase is very secure - so it is vital that your 12-word pass phrase consists of random 12 words from the word list.
Selecting passphrase for a new wallet
When you create a new wallet, you can click on the “reload” button until you see a pass phrase that you like. Still, it’s marginally safer to use the first one you see.
very very very very very very very very very very very stupid
is a valid passphrase. It is valid because any 12-word combination from the 1626 word list is valid. It would be very stupid to use it though If someone else ever picks the same passphrase they get access to your funds. Even hackers may try to do so automatically.
If you do want to pick your own phrase, consider rolling dice. Use four dices in different colors, and add the results like this:
This number corresponds to a word, ref this list. Repeat 11 times to get a full 12 word passphrase. This method can give 1296^12 equally likely outcomes. This is very good, however only a subset of the 1626^12 possible combinations.
You can play around with some passphrase tools I’ve made