fuel pressure regulator question..

[Carlitos]

hey guys..
i was just wondering if a car has an after market fuel pressure regualtor and the ecu was programmed for it, if the stock regulator is put back on and the ecu is not changed would there be any problems with the engine or anything?
any info would be appreciated thanks

[Carlitos]

if it was raised wot would it cause? run rich? idle problems?

[Limbo]

run rich clog up injectors, foul o2 sensor, etc.....