Import all Garmin data - does it overwrite?

Yesterday I started using intervals.icu. I uploaded my activities and wellness status of the last year.
Afterwards, I made some changes in the settings, for example my heart rate settings. I think the changes in these settings only apply to future workouts. But what happens if I import all Garmin data? Does that overwrite my uploads from last year (I hope!) or not?

And if it doesn’t overwrite. What can I do best? Create a new account? Or is there a way to delete the data of last year?

Furthermore a side question: How is me weight determined on days I didn’t weigh? On a Friday it was 85.8, the Tuesday after it was 86.8. On the days in between it says my weight is 87.8?

Importing all Garmin data won’t overwrite duplicate activities. It will not import the dup.

Changes to HR zones etc in /settings only apply to future workouts. However you can use the “Update Activities” button to apply the current settings to all existing activities.

You can also select activities in the list view to do the same with more control:

Weight is carried over from previous days as needed. Not sure where that 87.8 came from. You can download and upload wellness data in CSV format to bulk fix weight problems (Options → Wellness → Download CSV on calendar page).