Absolutely not. The reduction to a disorderly conduct is a bargain. In return for the reduction you accept responsibility to a different summary offense that may not technically fit the underlying facts and circumstances. Be aware that a Disorderly Conduct summary will not be eligible for expungement for five years; the Underage would be after you turn 21. In addition there is yet another option that would result in no conviction but you would have your license suspended for 90 days. You might want to talk with a qualified criminal defense attorney to help you with determine the best strategy. Talking privately with a knowledgeable lawyer beats the Internet every day. Good luck.
The condition for dropping the underage drinking is to plead guilty to the disorderly conduct. You can't have it both ways. The reason this is a bargain is that the underage drinking will come with a suspension of your driver's license.
This is not intended as individual legal advice and there is no attorney client relationship established by this answer. It is advisable that you seek individualized legal assistance. This is not a substitute for hiring an attorney.
I believe that legally, you can plead guilty to Disorderly Conduct and then appeal to the Court of Common Pleas and argue that the elements of Disorderly Conduct were not made out. I've seen this done successfully. I'll warn you though that Judges will hate this approach and may find you guilty just because they despise this type of defense. They might also permit the DA to amend the charges to Underage Drinking and proceed on those charges, though I believe that would be an improper ruling. More importantly, you should watch the video at the link below, which addresses the huge risk you may be facing if you opt to plead guilty to Disorderly Conduct.
Please note that I am only licensed in Pennsylvania. Therefore, if your case involves another jurisdiction, you should disregard this post. Further, this posting does not constitute proper legal advice since I have not been able to learn all the circumstances of your case. As such, you should consult a lawyer in person immediately for proper legal advice and should not rely on this posting for legal advice.