Does this also apply to business purpose loans as well? For example, if a borrower is refinancing a multifamily dwelling to improve the heating system, according to the revised rules, would this would be coded as a refinance, since refinance now trumps home improvement?
Yes, it applies to business purpose loans too. And yes, your example is a refinance.
When would we report a business loan as a home improvement?
If I applied to received funds to remodel a rental house or apartment building (new money - nothing refinanced or purchased with the proceeds). That would be a home improvement purpose but a business purpose loan.