Yes. So I'm going to use French here as an example, seeing as you have studied it. [L'homme fier - the proud man] "fier" will change pretty greatly depending on the noun that you use here. Let's take a look-
L'homme fier La femme fière Les hommes fiers Les femmes fières
As you can see, depending on the gender and number, at least in French, the adjective will change to agree with the noun it modifies. The same kind of idea happens in High Valyrian. Let's take a look-
Vala kastooba Valii kastoobii Vale kastoobe Vali kastoobi
Depending on the usage of the noun-adjective..."phrase" (?), the adjective will change to agree with case, number, and gender. I hope this helped!
Yeah the words change around a lot in High Valyrian. For example, the adjectives change based on the case and the gender. Have a look here to see what I mean for Kostobe:
They do match in gender, case and number, but there's only one declension per gender for adjectives. Adjective declensions differ based on the adjective's class. Kostōba is a class I adjective, which means that lunar accusatives always end in -e (sg.) and -ī (pl.).