I'm basically looking for a translation for the Swedish word "böja" (literally "to bend") in the context of grammar.
This verb is used generally for when words change according to grammatical rules, here are some examples when I translate literally from how I would use "böja" in Swedish sentences:
In present continuous, the verb "run" bends to "running".
The genitive bending for "James" is "James's"
The plural bending for "umbrella" is "umbrellas"
So is there such a general grammatical term in English? Even if there isn't that much use for such a word in English grammar - you don't have to deal that much with words that change according to clear rules - it ought to be practical when studying or discussing other languages, especially ones that have many cases and genders.