I need to add fat to ground pork for making Italian sausage. Can I use lard? Bacon fat adds the wrong flavor. lard?

If I were you, I would ask the butcher to sell you fatback or pork belly. They typically would trim that away for making carnitas and chicharrons, so they do have it. Failing that, I would suggest adding in olive oil along with the water you'll use to add moisture. You won't want to grind it with the pork, but rather mix it in with ice cold water you will need to make the mix emulsify better.

Lard is rendered pork fat. Rendering changes the texture and makes it likely to smear during grinding. I would try and find some fattier cuts to incorporate, or even just fatty off-cuts.
Sources:
https://nzcasings.co.nz/blogs/sausage-making-blog/why-is-fat-so-important-for-sausages#:~:text=Can%20I%20use%20lard%20in,is%20not%20suitable%20for%20sausages.
https://www.reddit.com/r/sausagetalk/comments/dosluu/is_lard_suitable_for_use_in_sausage/