I assume that you already know how to add grid-lines to your Revit project, but i will walk you through the proper steps to do so, just to double check.
How to add grid-lines in Revit?
- On the ribbon, You have two options depending on the function:
- Architecture tab
Datum panel 
(Grid) - Structure tabDatum panel (Grid)
- Click “Modify | Place Grid tab
Draw panel. - At this point you can choose to sketch your grid-line or pick lines .
- Now that we have looked at how to add those grid-lines properly, it is time to look at how to edit them and solve issues related to the grid-line heads (bubbles):
Check what symbol is used under the Type Properties window. As shown in the figure below.
So, what we did right now is checking the nested family used in your grid family, which is shown under symbol, and in my case it is “Grid Head – Circle”.
Now, i need you to go to your “Project Browser” Panel, and scroll down till you find 
, click on the “+” sign and search for the “Grid Head – Circle” Symbol under “Annotation Symbols“.
Once you find it, you can edit it by clicking a right click on it and modify the family then upload it again to the Model or duplicate it and customize it the way you want.
I hope this post is helpful for you. Please feel free to comment below if you have any questions.
Also, it would be great if you check Autodesk, they have great tools that are really helpful!
