Can I register 1 apartment as my residence and another studio flat as my my office?

Can I register in the same city 1 apartment as my residence and another studio flat as my my office? The city council send me a letter asking me if I moved out of my Current residence because I rented a studio flat within the same city, I'm using the studio flat as place to study and work at night so I don't bother my family at night. Any one know what would be the implications of my current setup?

can you tell them that 2nd one is your holiday house ?

Just tell them what you told us. There is no need to register your office.

Unless you're fluent in at least one of the official languages and you know your way round the Zivilgesetzbuch, I wouldn't advise lying to any official. It generally doesn't go down well and is frowned upon.

Here's how that conversation might go:

'Hello. Am I allowed to rent a studio in the town where I live so I can go there on holiday?'

'So you're telling me that you want to go on holiday to a studio in the same town where you live, possibly only a stone's throw away from your larger apartment. Really? Are you sure you don't want to rent it for some illegal activity, such as growing weed or prostitution? Wait here while I get my supervisor.'

I can't think of any reason why you shouldn't be able to rent a studio legitimately. Just go to the Gemeinde and ask.

Alternatively, you could check out desk space rental. I've had a quick look but wasn't able to find anything in Lenzburg. I found this in Aarau:

https://www.aaraudigital.ch/coworking-space/

CHF 390 per month or CHF 35 per day.

Sorry, not available in English. Use copy/paste in deepl.com

Thank you very much, I will just tell them the truth which is that the 13 square meters studio I rented is a place for studying and working at night let's see what happens.