I've filtered my Gmail inbox before in all possible ways, but only recently I've had a lively group conversation that got flooded by a single sender. I have tried different things only to find that filters are applied to entire conversation and not matched messages only.
I want to keep all the messages for the record, but I really need to move that sender's posts out of the conversation in order to maintain readability, while keeping the conversation going.
Is that possible in Gmail web at all?
I'm afraid that filters only work on messages as they come in. You'll need to manually delete that person's messages from the conversation.
You might temporarily turn off conversation view, search for and delete that person's messages in bulk, then turn conversation view back on. That way you'll be sure that you're only deleting that person's messages. Gmail should string the conversation back together after.
Gmail group messages in conversations by their subject, so it's not possible to move out a message by using the web user interface as it doesn't have a feature to edit the receive message subject.
To edit the message subject of the sender that you would like to move out from the conversation you could try to use an IMAP client that allow to edit message properties like Microsoft Outlook.
I did the above something similar several years ago, but not recently.
