Switch Sim to send SMS in a conversation

I have an SMS conversation which uses business line, can I reply to conversation using personal line without clearing conversation?

Here's a more clear picture:

I have my phone set to default to my personal line when texting. I also have gone into several of my contacts and changed my preference to text/call them from my personal line instead of my business line. However If I have previously started a conversation with them via text from my business line it will default to that line instead of my personal line. Leaving me unable to change my preference of which number I text my friends from. How do I change this?