I'll tell you what I do, from my phone the best I can without pictures.
So we can sink post into concrete without breaking the rail macro here's what I do..
Insert a small plate (4x4 or whatever) at the bottom of the post so the top is flush with top of concrete. Move the plate vertically down into the concrete whatever depth you need. Copy this plate around to the posts you want to sink into the concrete. Use the cut by member command. It's next to the miter command on the menu. This will extend the post to the plate without breaking the rail macro. Don't enable the weld or else it will become part of the rail.
I put the plates on the not visible role and unchecked the behavior for numbering etc. If you tweak your field drawing detail style to turn off the objects on the not visible role then it's like they are not there and your posts are sunk into the concrete. I actually added a selection filter to my template so I can select all temporary modeling items and hide them in the model so I don't have to look at them.
I actually do the same similar using flat bar along the edge of slabs so I have something to fake the railing macro to. It's easy to put a 6" wide bar down and have the rail align to the center of it. This way I can also determine where I want rail splices. Split the bar wherever you want a rail splice. I would just copy the flat bar down 4" to get the embedment and cut to that member with square end cut.
Hope that helps someone 😜
...and fix the kiss export issues.