The owners have evidence that they bought the land from the municipality of Carolina PR but they never add it to the hard copy of the property.Any advise on how to modify the hard copy or how to deal with this to be able to get the loan?

Go back to the seller with slightly modified terms.

I've been looking at Lease Runner for their lease (pre-built for our state, but also modifiable), $30/group for electronic signatures.

They might send notification if the the policy is being modified (ie. change in dates, limits, etc.).  

@Morgan Klein allowing the tenants to modify the lease before they move in is a slippery slope.You (or the PM) is essentially training them in a subconscious way that the lease terms are negotiable.

Boxwell: https://boxwell.co/, or Janus - Mass Relocatable Storage Units) which brings the units in on a pallet and then get they get assembled either by you or one of their specialists.If you want true shipping containers, there are many folks out there modifying and supplying these that it's better to search locally. 

I just put another building under contract yesterday, One the PAR contract It specifically states that the seller does NOT have the right to the appraisal, (on page 6 of 13).As @Chris K. says (my modified version) "although I'm NOT a lawyer, I did say in a Holiday Inn at one point".

@Paige Roberts I would modify your lease to prevent this in the future.

It is still being modified but as of now, they will be limiting the density of STRs to 1 out of every 8 houses on each block face--if you don't get grandfathered in.

We’ll reprice it at that time to whatever the market rate is doing, and modify it for another 5 years, and so forth.