Unitals and replaceable t-nests

Let U be a known unital of PG(2, q), q odd, and let N be a t-nest in a regular spread S. Suppose we replace N by a replacement set N to form the new spread S ′ = (S\N)∪ N ). Using the Bruck-Bose correspondence, we look at the affine points of U in P(S) ∼= PG(2, q) and see whether the corresponding affine point set in the new plane P(S ′) can be completed to a unital.