Just to clarify, you get boots loaned to you for the elements of PRMC that require them for the Health & Safety aspects. You will not run any great distance and therefore do not need to take your own boots & are advised against training in boots before PRMC. You cannot therefore use your own.
POC candidates are encouraged to take their own boots as they will be wearing them a great deal more & are expected to be at a higher level of preparedness overall. Officer candidates are advised to to only train in boots for the bare minimum, just to get used to it, but not to the extent that they regularly exercise in boots.
Running flat-footed in boots is one of the biggest causes of shin-splints and for that reason alone, if you don't have to, don't train in boots until you actually need to.