Stem changing in the present subjunctive is not any harder than conjugating in the present tense.

The rules are the same as regular present tense conjugation.

If the infinitive stem changes in the present tense, it will in present subjunctive.

Nosotros and Vosotros still don’t make stem changes

*-ir stem changers have a different set of rules!

Examplequererquiera / quieras / quiera / queramos /

queráis / quieran

acostarseme acueste / te acuestes / se acueste / nos

acostemos / os acostéis / se acuesten