If you have not been accepted in the University, I don't think you can 'break in' and access the altars. (All my characters enjoy the mages guild, so I have never tried to break in.) I'll be happy to stand corrected if wrong and hopefully another poster can verify this.
Ways to access spellmaking/enchanting altars include:
- Complete the simple quests to enter the University (even simpler if you fast travel).
- Install and upgrade the DLC Wizards Tower.
- Bring up the desired altar menu via the command console (if on PC).
- Mods that provide alternative access to the altars (if on PC).