As you already found out the grid marker is a fairly standard GDL object. However, and this is a bad design choice and should be addressed by GS, you can not choose a different marker.
I had the same issue a couple of months ago and had to resign. I tried a lot of shenanigans but I have to conclude that it seems impossible to get to deploy your own marker.
Please GS! Make a nice little button there so we can choose between markers! Maybe in AC24 update 3, huh?
AC 24 [ger] | Win 10 | Developer of the GDL plugin for Sublime Text | «Furthermore, I consider that Carth... yearly releases must be destroyed»
In the meantime I saved the grid object as a new one, changed the object subtype to "Model Element" so I can place it individually, manually re-entered the AC_ variables (is there a way to keep them when you change the object subtype?) ...but I'm not sure how the section/elevation display is handled, it doesn't show up there.
I also have weird glitches with the text display in floor plan - if I zoom out, the grid name disappears.
I think it wasn't meant for "standalone" use.
actively using: AC22-25 INT | Rhino6-7 | macOS / win10
Thank you very much for sharing your wishes and requests, and for those of you who voted to express their opinion.
I am happy to say we took notice of this wish and I have added it to our Wish List database (please refer to it as Wish #12950). Hopefully, our Product Management team will adopt this one in the future. Personally, I definitely agree with all points above!
Thank you all once more, and I wish you a great day!