Normal characters are (汉)字 and nonstandard characters are 俗子.
Wrongly written words or nonstandard forms of written words can be referred to by using 俗作.
For instance, the entry for 耳食 in《南充方言词语考释》says:
What are these types of words called?
异形词 is an, obvious, option. I would like to be more specific noting that it is a 俗 problem.
俗词 would just talk about current terms or expressions, vulgarities or familiar language.
What is the proper term for nonstandard forms of written words?