Adding Activities Versus Petition Amendments
While you should do your best to disclose in advance all the proposed activities, artists and entertainers may add or subtract performances involving similar services without filing a new petition, provided the new activities take place within the classification period and on behalf of or in association with the same petitioner. O-2 accompanying aliens are subject to the same restrictions.
To be clear, subject to the discussion of Selecting Who Will File the Petition and Multiple Venue Petitions, if the newly added performance or event involves a new, direct employer of a beneficiary, USCIS must first approve a new petition by that employer to enable the beneficiary to work for that employer, though subcontracting arrangements might be possible. If, however, the newly added performance or event is for the original petitioner, who is a "management agent" or an "appointed agent," and involves the same or similar services at venues other than those disclosed in the original petition, during the original classification period, then provided those activities occur through or under the auspices of the petitioner/agent, the beneficiary may undertake those activities without a new petition.
What constitutes "similar" services is a matter of USCIS discretion. An O-1B concert hall soloist can add engagements in concert hall venues without concern, and most likely dates in smaller, more commercial or academic venues as well. It would probably be acceptable to USCIS were the soloist to play different music, jazz instead of classical, for instance, on those added dates. The soloist would still be playing his or her instrument, before a live audience attracted because of the soloist's reputation with that instrument, even though the soloist's O-1B reputation was gained by performing classical music only. It is less clear whether that soloist could add dates to perform as a member of a jazz ensemble. And it is debatable whether that soloist could add studio recording dates without additional action.
Where the artist's or group's principal purpose for being in the U.S. has materially changed, the petitioner must file an amended petition. An amended petition in this case simply means that the petitioner will check off Box 2c ("Change in previously approved employment"), in Part 2 of the I-129 petition, and also request an extension of stay (Part 2, Box 4c). Otherwise, the petition substance and process would remain the same.
Note that if added or future engagements will take place in conjunction with another employer or agent altogether, that party must file a separate petition, unless the original petitioner filed an itinerary-based petition, including a cover letter that allowed for additional engagements to be added. For example, if an artist changes management companies mid-stream, the new management will need to file its own petition. This, of course, would not be an amendment.