I use the disconnects on 2 pumps, the cooling pump for the refrigerator and the potable water pump. Both of these pumps could fail when I don't have the resources to properly connect them with heat shrink butt joints and and I can prep the replacement pumps well before they are needed. Otherwise I use butt connectors unless there just isn't enough of a service loop and it is too difficult to run a longer wire, so far one cabin fan has this treatment.
I don't understand the scenario, I think.
- You have a spare pump with a matching connector on it (you would have had to do this. because they don't come that way) and ...
- ... your tool kit does not contain crimpers and fittings. Nor do you have Wagos or a choc block you can snap a section of. Seem unlikely.
If the wire is too short, sounds like a good time to add an extension that will make easier to reach.
Just sayin', I've had quite a few quick connectors pick up resistance over time, over the years, but never had a butt splice fail. Boats and industry. If you need heat shrink over the connector for reliability, then you need a butt splice, which is simpler and more reliable. I'm not going to frog around trying to remove an adhesive lined heat shrink from over the connector (what the OP was suggesting) without damaging the wire or connector, while working in a tight space without enough slack to make a butt splice. I don't see how this senario adds up in the real world, and it is not a practice you will see in industry. If the equipment comes with spades attached, I will use them, but that is pretty much the only time.