I nearly always disconnect the hose reel before reeling the microbore back in. One of the reasons I do this is it allows some of the water to drain out of the hose reel so that when I lift it back in the vehicle, water doesn't drip out of it. In light of the above thought, it also allows you to reel back in unpressurized microbore.
You should already have a pressure switch build into your pump as Nathanael mentioned but unless you disconnect the hose from the source of the pressurized water, it will naturally stay pressurized.
What make of microbore is it?