For sure you have complete freedom to create what you like. Originality prevails.
By "copyists conventions" I was referring only to the graphic elements that make a score readable and playable by performers other than yourself: mechanics such as indicating key signatures, clef signs, rests, repeat signs, etc.
All the details of notation that music copyists, type setters and proof readers work to perfect prior to publication. At least that was the case in the old days.
In the 21st century I guess music notation programs have simplified all of this for computer literate composers.
All the best!