Absolutely! If your record is eligible to be expunged under current Pennsylvania law, you can continue to file for expungement even after Clean Slate goes into effect. Clean Slate/Limited Access merely shields the public and potential employers from seeing your criminal record, but it does not destroy the record. Expungement is the only mechanism to permanently and completely remove criminal history record information. Petitioning for expungement greatly increases the possibility that your past doesn’t harm your future!
Note: you can generally seek expungement for cases in which you were not convicted (e.g. charges were dismissed, withdrawn, nolle prossed (never processed), or you were found “not guilty”), diversion cases like ARD where you have completed your sentence, and summary convictions after five years without arrest.