-- Alter any records needing update
update table1 set
   ....
   property_id = T2.id
   ....
from table1 T1
join #HOLD H on H.PrimaryKeyColumn=T1.PrimaryKeyColumn
join table2 T2 on T2.property = H.property
where T1.property_id is null or T1.property_id != T2.id

-- Insert new records
insert table1 (..., property_id, ...)
select ..., T2.id as property_id, ...
from #HOLD H
where H.PrimaryKeyColumn not in (
   select PrimaryKeyColumn
   from table1
)