If am not mistaken you want all your change to be sent to a single address, then the solution is to import the individual private key of that address into electrum this will make electrum to send the change to where the bitcoin is coming from. But should you import the seed phrase then I think it will definitely generate new change address for every new transaction having a change as that is the protocol of an HD wallet format.
I think I have found the a way for to specify the change address should you import the seed phrase. Follow This guide below, the two address there means you are sending to two output address plus the the specified changed address of your sending to just one then it should be one address and then the specified change address which
Must end with Exclamation mark
To use a specific address as a your change wallet you can use the "send to many" feature. In the "send to" field you can list multiple addresses, followed by a comma, then the amount you want to send. Use a exclamation point for the last address, which will be your change address. The exclamation point will select the remaining amount, minus fees to send to that address.
Example:
1xFirstPaymentAddressxxxxxxxx,0.0035
1xSecondPaymentAddressxxxxx,0.004
1xSpecificChangeAddressxxxxxx,!
Electrum will show you the outputs before you confirm them, and you can double check the addresses there. If the change address is in your wallet it'll be highlighted in green. The change addresses created by Electrum will be highlighted in yellow.
