When I import new contacts in Hubspot, I would like the old properties not to be overwritten by new one.
Hi @hannas
Thank you for reaching out. Your import file will deduplicate contacts based on the email address (or the Contact ID if you’re using that). In that case, cells with values in the excel will update the existing values of this contact. The only way to not have that would be to create duplicates records or to leave the cells blank.
I want to share the following resources with you for more information and specifics
Import | Frequently Asked Questions
If you want to add values to existing checkbox properties values, I want to share with you this resource:
Import data to checkbox properties
Hope that helps.
Have a lovely day,
Tiphaine.
Hello Tiphaine,
Thank you for anwsering me.
Somehow, I might have put it in the wrong category, as it’s a feature request and not a question (I know it’s not possible in Hubspot, but it is in Pardot) 
Where would be the right place to post it?
Thank you,
Hanna
Hi @hannas,
It’s been a while since you posted this but I wanted to share an update: This is now possible! During the mapping step of the import process, you should see the option to not overwrite existing values:
If this answers your original question, you can help the community by marking this post as a solution.
Cheers!