Bit confusing that post!
So, you're getting them to mole a new main in, in mdpe? Or are they digging a trench?
I'm a Gas Safe plumber, heating engineer and drainage guy by the way, so I know what's what :)
Most custards don't!
And is why it's standard practice to add 20% when supplying... But that is like forbidden fruit, nowadays, when customers think they can save a few quid by ordering stuff online!
Trouble is... The online suppliers don't have a clue what they're selling and don't care!
The only reason that you set them to high/max/5 before removal and replacement is that it moves the internal plunger further away from the pin in the body which is/should be spring loaded... Thus you're not pushing against resistance as you try to refit the head.
Do tap the pin gently before...
Up to you, but I'm a plumber and when customer buys it, they carry the can for any problems with the product.
Either way, make sure you flush them out before fitting... Many of them are full of burrs, rust and manufacturing debris