Can I withdraw a pending I-829 application and re-apply for another type of green card while in the U.S.?

Yes, you can do this but keep the pending I-829 until your interview with your spouse and then withdraw and abandon permanent residency.

In order to adjust the status, you have to be in a valid nonimmigrant status. Since you are already a green card holder, you have to leave, surrender your conditional green card and then apply for a new green card through your spouse.

There is no need to withdraw your application. You can simultaneously pursue both options. However, if one immigrant visa is approved, the USCIS will certainly cancel the other application.

It is not a good idea to give up a pending I-829 unless it is very clear from the record of the case it should be withdrawn because it is not approvable as filed.

You have asked a few questions here. Of course, you can get married with your fiance. There is no need to withdraw your pending I-829 petition to get married. Once you are married, though, you will be eligible to apply for permanent residency as the dependent of your wife. The key is to make sure that you are not in the U.S. without any status. Once you obtain a green card through your wife, then there is no danger dropping the conditional green card you currently have.

After you file an I-485 application, you become an applicant for adjustment of status.

Should you enter into a bona fide marriage with your fiance, you could withdraw your I-829 petition and apply for adjustment of status, as a dependent of your wife, under her E-2 preference petition.

Keep the I-829 and file for your I-485 after you marry.

There is nothing preventing you from having two petitions for a green card (EB-5 and fiancee). As long as you qualify for both you can have both pending and go with the one that''s approved. There is no need to choose.

Feasible yes; immediate no. Do not give up your conditional permanent residency until you have the other green card secures. Get an attorney who can walk you through the process.

You certainly can marry your fiance and file an I-485 along with your fiance based on the EB-2. Whether and when to withdraw the I-829 are different questions and the timing and potential future backlog of the EB-2 come into play because you do not want to have a time when you are not a permanent resident.