o The SRS HIC component (4/5) on the back of the instrument cluster stands for High Integrity Circuit -I had to look that up. There are various HICs used in SRS safety systems. In some, it's a second barrier to prevent an accidental discharge. In this case it's a safety circuit to make sure the SRS controller indicator lights if the controller is dead and unable to sense a crash as well as when a problem is detected by the controller. It's connected to SRS controller pin 1, which is an output from the SRS controller to say everything is okay. If that signal is missing, the HIC provides ground to the SRS lamp to illuminate it. It's a very simple circuit and not a known problem area, neither are SRS controllers unless they have been in a crash or been physically damaged such as being dented during seat removal (which along with any underbody deformity technically requires control module replacement no matter how slight the damage).

o Your clockspring remains a high suspect for the SRS light remaining lit. It would be nice to have the OBD code to verify this, but without a code to suggest otherwise I'd throughly test the clockspring and connections to the airbag. When the clockspring goes, the spring with the conductor wires for the air bag breaks, usually a total break meaning there will be no spring resistance, but it may initially be a partial break possibly affecting just one of the spring conductors. It sounds like when you checked the horn button ring circuit that you also checked the integrity through the clockspring of the two air bag wires in the orange connectors. If you got connectivity through the clockspring on the orange and orange/white wires on both ends then you need to follow up on that to make sure conductivity remains constant throughout the range of travel from lightly to tightly wound. That requires unlocking the clockspring. No problem to unlock it, just make sure when you re-lock it that it's in the neutral position with enough turns in the spring left to allow the steeering rack to reach end of travel well before the spring is fully tensioned, and in the opposite direction that the spring remains partially tensioned at the other end of steering travel, not fully or overly unwound to stress the spring in that direction. Basically you count the turns from fully relaxed to fully tensioned and lock it at the mid-point. If the mid-point is close to the locking tab, like within a 1/4 turn, then use that lock position, otherwise unwind it to the next lower lock position.

I knew I'd mentioned the clockspring to someone in recent history, but forgot it was you with your horn issue rather than someone with an SRS problem. Yes, there's somewhat suprisingly no horn relay as in older cars, which would likely have provided more power to the horns to get a louder and throatier beep rather than a roadrunner "meep". Probably a European thing, not DOT.

o For the hub studs, the proper way is to remove the hub and use a bench press. Volvo has a special tool (2862) to do this on-vehicle, basically a special c-clamp press designed for this purpose. I doubt there's a universal tool that's similar. The FAQ describes trying to drive them out with a hammer and pulling them back in using the lug nuts and a spacer https://www.brickboard.com/FAQ/700-900/WheelsTires.htm#WheelStudRepair. Doing it on-vehicle, I wouldn't get too carried away with a hammer on a badly stuck stud for the sake of the bearings. I see there's a universal stud insert tool listed on FCPEuro, Lisle 22800. It's just a spacer with a tapered hole at one end to accept the taper of a lug nut and help keep the stud straight during tightening. Any similar solid spacer should do, like one or two oversized nuts. Replacement studs are commonly available, p/n 1359905 for the fronts, 1209295 for the solid axle rears, 3516057 for the multi-link live axle rears.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now