We have a loan to refinance some farm ground we did a loan on a few years ago. At the time, there were no dwellings on the property. Now, the borrowers have moved a titled mobile home onto the property. The appraisal notes it is "personal property". Does our original loan become dwelling secured when they moved the mobile home onto the land we have as collateral?

You say it is a "titled mobile home". Just because you have the real estate doesn't mean you have the MH, since it has a separate title. If not, your first loan is not dwelling secured. Therefore, a refinance of it would not meet the definition of "refinance" for HMDA.

If you do have the MH as collateral, and you will on the new loan, then you do have a "refinance" for HMDA (dwelling secured loan replacing a dwelling secured loan).