In general I tend to charge 500cr a day for skilled shipyard labor.

* Conversion of cargo space to fuel tankage, or vice-versa

* Conversion of passenger space to cargo space, or vice-versa

* Cutting new hatches into the hull, for access to converted space

* Replacing a turret - don't consider the costs of the turrets themselves
or the weapons mounted, just the actual cost of dismount/mount.

All at yard labor rates, generally 50 dTons a week of change.

* Pulling large drives or power plants in favor of smaller units, and
mounting the smaller units - again, don't considerr the costs of the units,
just the cost of dismount/mount. (It might be acceptable to say "You Can't
Do This!")

* Conversion of general passenger space (e.g., staterooms, commons) to
specialty passenger space (e.g., sickbay)

Stuff like this at cost of the new equipment plus the labor rate of removing the old equipment.

Related question: What would be the costs (relative to new) of
used/reconditioned units (where appropriate) salvaged from hulls otherwise
being sent to the breakers?

Generally 50% of new. Using the the repair rules.

In short: Assume I have a used ship in good condition free and clear, but
it's not the _right_ kind of ship. How do I figure the cost of repurposing
it to my needs?

As for time needed for a conversion it is a minimum of a week per change.

Evyn