Not all yards are the same. There really is no "usual" procedure these days. Some yards let you do what ever you like yourself but require that contractors you bring in have insurance (at different levels depending on the yard 1,2, or even 3 million in liability is not unusual). Some yards won''t let you work in the yard but will let you hire them to do it. they don''t have to let you bring in contractors and one yard near me would tack on 30% if I went there and used my own contractor.
In general, nothing is "understood" it''s all supposed to be spelled out in your contract.
The yard I use now charges for al things they do but let you do all you want yourself. You can buy supplies where you choose.
So like now. They hauled, blocked and will launch when I''m ready. My own contractor painted and di some engine work and will charge me direct with no yard markup. If I did it myself I could have brough in my own paint and done the work myself.
The real difference is they will probably charge a small amount for storage for these past few weeks but they wouldn''t if they did the work.
You just need to find out before you bring your boat there. They don''t have to let you do much of anything on your own if they don''t want to.