If I Re-enlisted for a duty station as an E5 ( non promotable) and I promote to E6 before my report date, will my pcs orders change ?

Generally no, not for the location. Your specific assignment will likely change, but the Army will do everything possible to meet the reenlistment option (sending you to the duty station).

If it is just not possible to do so (there are no assignments for SSGs of your MOS or branch immaterial SSG positions that won't adversely affect your career), then "something else" will happen and varies from re-negotiating with you, having higher authority sign off on options, etc.
-------------------------------
* https://armypubs.army.mil/epubs/DR_pubs/DR_a/pdf/web/ARN14314_AR614-200_FINAL.pdf

Possibly, but not necessarily. Timing is certainly a factor because takes a while for the system to notice the change in your rank, then see if there is a valid position for you, then do something about it.

If the Army decides there is no E6 slot where you are going, the orders are supposed to be changed. If everything is done perfectly someone would look for a new assignment for you that still fits the duty station you reenlisted for (but of course there is always that fine print about "the needs of the service").

I had something like that happen to me a long time ago (1975) when I reenlisted for an accompanied tour in Germany then the Army changed my orders to an unaccompanied tour in Korea. By the time they approved cancelling the reenlistment I had been in Korea for several months and was about two months past my ETS date. I ended up reenlisting for present duty assignment.