Some people add or change letters that aren’t in a word or name, i.e., “Simonese” cat instead of “Siamese” cat, and French “provinincial” furniture instead of French “provincial” furniture. Also adding letters in the middle of a name, such as “Stolperman” instead of “Stolpman.” Is there a word for such misuse of words/names?
Maybe epenthesis, which Wiki describes as “the addition of one or more sounds to a word, especially to the interior of a word”. See here.
This might not be exactly what you’re looking for though, since from what I can tell this is taken to be primarily a phonetic phenomenon.
For example, this site on rhetorical schemes claims that a poet might use visitating over visiting (in speech and orthography) in order to preserve their meter.