There is a simple equation here: "Pay peanuts get monkeys"
You have already dug yourself a hole here by saying you need someone who can change a cylinder liner, then go on to say they must have good electrical skills, while lambasting yacht engineers for working on auxiliary things too much.
A Deutz 628 isn't that different to any other diesel engine, it runs by compression ignition, the crankshaft goes round and round and the pistons go up and down. What's the "specialist skill" required to change a liner on this engine. If the guy can do this he will also need to adjust the valves when the cylinder head goes back on.
On your blog you say it was recently overhauled so an internal component inspection is probably not something you need to look at in the near future.
You will find that your carefully low cost converted trawler has other problems far removed from the Main Engine, reality bites in that you really need to find someone who can take care of the Auxiliary things and has a basic knowledge of medium speed small bore engines in preference to someone who can do crank deflections while the engine is running!
I intend no offense to your question, I am an Engineer originally(with a valid STCW95 Chiefs ticket) myself so I speak from experience