Yes, that's correct! The verb "preferir" is a stem-changing verb (or a "boot verb") in Spanish. It undergoes a vowel change in its stem when conjugated in most forms. Here's a brief overview of how "preferir" is conjugated in the present tense:
- Yo prefiero
- Tú prefieres
- Él/Ella/Usted prefiere
- Nosotros/as preferimos (no stem change)
- Vosotros/as preferís (no stem change)
- Ellos/Ellas/Ustedes prefieren
As you mentioned, the "e" in the stem changes to "ie" in all forms except for the "nosotros" and "vosotros" forms. If you have any specific questions or need further examples, feel free to ask!