Though it's worth noting that Green Sun Princes can be lied to and manipulated as long as they still willingly agree (so if they don't know the demon offering it is actually a demon they may have completely the wrong perception of the situation), and that while Abyssal Exaltation involves an supernatural and at least some degree explicit oath of service to the forces of Oblivion, it comes under hella duress since the only other option is "finish becoming dead".
Indeed, they can be lied to, but the being offering the exaltation is only allowed to use natural mental influence. No mindwhammies or anything, but people will often take that power anyway. They don't want to die, or they want to fix that mistake, or they never want to be powerless again, understandable motivations for accepting.
They'll still have a vauge idea of what they are, after they accept.
Does the memories of the past screw with the present?
They can, depending on what version of Past Lives you took, and how much you took. Stepping into the ruins of Meru and seeing flashes of the city as it was during the First Age is a bit of flavor but doesn't really screw with you.
Going "That's
my ship" when you encounter a First Age fast cruiser screws with you a little.
Having the memories be so strong that you sometimes respond to the name of your last incarnation screws with you somewhat.
Waking up one morning and going "Who the hell are you, what did Little Sun Dragon do with her hair, and where are my Gens?" screws with you and your fellow players a lot,
and makes for some great RP fodder.