Can a SPAC's pre-offering shareholders (such as promoters) vote on the merger or exercise appraisal rights?

This is restricted. The Korea Exchange's listing rules prevent a SPAC's pre-offering shareholders, etc.

from exercising voting rights and appraisal rights in connection with a merger, and proceeding with a merger in breach of this is a ground for delisting. When disclosing the results of the merger shareholders' meeting, a SPAC must also state whether pre-offering shareholders, etc. exercised voting rights or purchase demands, whether the merger value is at least 80% of the escrowed funds, whether there is a special interest relationship with the merger target, and who is subject to post-merger sale restrictions and for how long. This mechanism ensures that the will of shareholders who joined through the public offering is reflected in whether the merger goes ahead.