If it doesn’t require a type and you are otherwise legal to fly it, log it as straight PIC time, no note or anything else needed.

If you have the category and class for the plane, it’s 91, and you’re flying it, that’s pretty cut and dry just normal part 91 flying regardless of whatever else the plane is used for


Frankly I think adding odd reason next to flights is going to cause way more issues than just logging a normal PIC 2.3, instrument .3, cross country 2.3 total time 2.3 type normal entry