Can I Re-Import XML without any other problems?

Hi i am quite new to this. The problem i have is that i exported my xml (all content) from my old free wordpress site to my new self hosted site a bit too early.. my older site has been getting more comments since so now i want to export those ‘newer comments’ to the new site. I have learnt that i cannot simply overwrite the xml of the new site without it duplicating the content.

My question: If i were to go delete ALL my posts/comments on my new self hosted site right now through jetpack (empty it out) and then re-imported the xml content all over again would this be a good clean way around this? And does re-importing ‘all content’ mean just the posts/comments or does it also mean other hidden code that could potentially mess up the site? Trying my best to avoid messing anything up.

Thanks for any help and advice you can give.