So my hunch is that either this isn't possible or it would require more mucking about with castes than I'm inclined to do, but just in case- with SP and Woohooer, is it possible to make only certain Sims able to get pregnant by/impregnate others of the same sex? (I've got a handful of Asari Sims running around my Lunar Lakes. For the non-Mass-Effect-fans around here, one of their species gimmicks is being able to reproduce with any sentient being, period. But I don't want my regular human Sims to be able to do the same thing.)

For any StoryProgression setting, including who can and can't get pregnant, caste options override town options.  So you might have to do a little bit of mucking around, but it shouldn't be so hard to create a manual caste, as in, you get to assign it manually to specific sims.  Then you can allow whatever pregnancy options you want just for those sims, and leave the rest of the townies to behave as normal, or whatever your current definition of normal happens to be.

The StoryProgression Interactions pages looks like it's intact now.  I think the setting you want is Pregnancy: Allow Can Be Pregnant.  You can also allow or disallow sims in a certain caste to be impregnated by sims of other castes (Pregnancy: Allow Can Be Pregnant Caste, the next setting down).

By the way, you can also set manual castes to be inherited, so the pregnancy options could behave as if they were genetic.  (Caste Options > Caste: Inherited)

Does "Allow Same-Sex/Same-Gender" in Woohooer override SP, though? I have it set to False over there.

The SP Interactions (Documentation) page says Woohooer is supposed to check SP settings.
Pregnancy: Allow Can Be Pregnant

• Whether the sim is allowed to be pregnant by any means, including pregnancies incurred beyond the purview of this mod
• If you disable this option, the mod will actively terminate any pregnancy the sim receives
• NOTE: This option is actively checked by Woohooer, and will block any attempts to get this sim pregnant using interactions provided by that mod.
• Default: True
• Hidden by: "Pregnancy: Allow Participation" = "False"

Alright, so if I'm following I'd need to allow same-sex TFB in Woohooer to make TFB/Risky available for female-female interactions, but as long as I left the default male caste alone in StoryProgression, I wouldn't wind up with a bunch of pregnant dudes as well. Might need to mess around with Allow Be Pregnant Caste to limit the shenanigans to Asari as intended. I think SP has an option somewhere to make same-sex pregnancies always produce a kid of the same sex as the parents, too, so I'd need to turn that on for extra authenticity (ie, they're an all-female species.) Tada! I'll give it a try.

Update: Well, that didn't work. Male-male interactions show "Progression Blocked" for risky/try for baby as intended, but I've tried it with various combinations of the following settings and human female Sims, without the Asari caste, can still get pregnant by other women:

Asari- Disallow Participation Caste: Female
Female- Disallow Can Be Pregnant Caste: Female, Asari, Allow Can Be Pregnant Caste: Male only

It's weird, because comparing that to the default settings for males, that *should* work.

Am having a little trouble following this, so bear with me. But if you have sims who happen to belong to the female caste (automatically, because of their gender) and also the Asari caste (manual), then the two castes may have conflicting settings for the same SP option(s) and you will get random results on those option(s) unless your Asari caste has been granted higher Priority within its caste settings than the female one. Also, you shouldn't ever need Disallow (x) and Allow (x) on the same caste as one should always override the other, no matter what "x" happens to be -- in the above example, x = "Can Be Pregnant Caste."

But if that's not helping, I would suggest testing the settings wanted on the Sim Options level first as Sim Options for individual sims will always trump Caste Options. If you can get them to restrict and allow impregnation as desired, then move back to the caste structure. What you may want to try if there is still some kind of logic trip-up happening is a Non-Asari caste or maybe a Non-Asari Female caste although it seems from the description that those shouldn't be necessary.

Sorry, wasn't sure how to explain myself better: in test female/female interactions, one with the Asari caste applied and one without, the one without got pregnant even if Disallow CBP Caste was set to block Female and Asari sims, if I tried setting Allow CBP Caste to only males instead (not at the same time), or if I set the asari to Disallow Participation with females.

Trying the same thing at sim-level options gets the same results... so maybe I'll just table this one for now. "Progression Denied" only appears if I entirely disable female sims' ability to get pregnant and, well, that wouldn't be great for neighborhood longevity

There'd be some manual fiddling required in any case (asari are supposed to always pop out asari kids = I'd need to hop into CAS to make them look the part anyway), so manually triggering a pregnancy here and there for story purposes isn't really a huge extra step. Just would have been cool to have it happen on its own.