i vaguely remember making a request or three about renner back in the day. if i remember right one of my better ideas was having renner switch her target for her yandere like obsession from climb to ainz via albedo talking him up and her being genuinely interested her new 'best friend's' husband/crush.
of course i'm not saying climb should be locked out of the romance with renner. but considering climb's feelings for her were based off respect. seeing how she's the one who initiated the romance, there would be no NTR to be had if she just fell for ainz instead. so it think some choice (or series of choices) made in game leading to renner falling for ainz could be a reasonable option to have.
supposing renner is considered for the harem, i'd also request some odd scenes with renner and albedo after she joins. how well would they get along? would they be 'best friends' still? would they scheme against each other for petty reasons? would they collude and plot together to have a slight bit more monopoly of ainz's time? i'm thinking this could be some prime character building or comic relief material.
As a Yandere fan, I personally find that type of personality (in fiction) nice due to their unhealthy obsession over a certain person, and their twisted loyalty.
I agree that killing Climb off would normally work (As it worked with Imina), however I'd need to be comfortable with writing rape, and I am not. It is also against the rules of the platforms I use, and due to her character I'd need to effectively understand the fetish and be able to write a very slow breaking in of her personality, which goes totally over my abilities as I am a very boring vanilla.
Switching target would feel like cheap writing since it is made clear that her obsession over Climb is basically set in stone. There are some obsessions that can switch target with ease (See Carrie Cutter character from Arrow), but that is definitely not the case with Renner.
Her loyalty towards Climb makes her sell the whole kingdom just to get protection for both, and even agree to a race change experiment.
Rather than ruining a character for the sake of adding +1 heroine when the series itself has already too many heroines, it's more of a golden opportunity to write a separate short game featuring Climb, with Renner as the only heroine.
Unfortunately while I love Yandere, I am not into nor I know how to write femdom very well, so that might take a while.