I guess the question should be. Do we get paid for our current replacement cost or the amount of work we do each day? Salaried jobs are treated differently than hourly jobs.
If we should get paid for value, your value arguably hasn’t changed yet as you take on this new responsibility. After you’ve done it for a while, yeah, you are now more valuable because of your new experience, skills, confidence gained, etc. But you don’t have those yet. So, maybe they are giving you an opportunity to build up equity in yourself and the cost to you is more work.
That’s one angle. But the other is that you are doing more work and maybe working more hours. If this is truly just more hours each day and not a slight shift in priority, then maybe it makes sense to at least have the conversation with them.
If I were you, I’d probably do the job first, do it well for 6 months and then have the discussion. Asking for money up front may be a little aggressive. But others may do differently and that is very important. Do what is comfortable for you. My sister is aggressive and talks to boss about salary all the time and she’s now making a lot of money.