I'm currently playing through ME1 for the first time and I'm planing to import this playthrough to ME2. I will probably play through the series several times to get different outcomes and I was wondering if it possible to get several different endings on the same play through by saving at a critical point, saving again afterward, reloading the former save and playing through that mission to achive a different outcome. If so how does this effect the character transfer to the next game? Will I be able to chose the ending I want or will it screw it up?
For example I accidentally romanced Kaidan cause I was being to paragon and now I don't even have the option to dump him

so I think I'll have to blow him up at Vimire. Later on though I might want to do a ME2 playthrough were I stay faithful to Kaiden just to see what happens in ME3 so can I just go back to a save before Vimire and get Ashley killed this time instead of doing another play through?
Thanks