The answer is yes for the first message of a conversation, but not for the comments or as a reassignment of the full original conversation to another subject.
Combining multiple subjects for a same message, or using only one subject allows for the same capabilities:
You can click the 3 vertically-aligned-dots on the conversation and then on "Post on other subjects":
This will create a new conversation you can comment and that embeds the first message of a conversation. You can post it on any other subject(s) from any of the workspaces you are member of.
You can then remove the first message using the x (only available if it's your message)