The “Increase today’s review card limit” custom study has only an effect when you have exceeded the “Maximum Reviews/Day” (set to 200 by default) but still have due cards in the concerned deck.
However, as I understand your situation, you want to study cards that are not due, yet. For that you can use the “Review ahead” custom study or create a filtered deck with “Rescheduling” enabled.
But note that this is generally not a good idea. You will without a doubt get some benefit from additional reviewing, but it’s far less efficient than if you adhere to the intervals scheduled by Anki. If you’re not pressed for time to learn these cards, you can most likely spend your available study time more productively.
Especially this part will not work very well. Let’s say you have reviewed some card yesterday and it now has an interval of 3 days. If you review it again according to schedule the day after tomorrow, it will then get an interval of about 7 days because you hadn’t forgotten it after 3 days. However, if you review it prematurely today, Anki can only see that you were able to recall the card 1 day later (and we already learned that when the card was reviewed the last time). So there’s no reason to increase the interval as you still have to prove that you won’t forget the card after 3 days.
(I don’t actually know what the scheduler will do in this paticular reason, maybe the interval will increase by a small amount, but that’s the gist.)
You can see, additional reviews are not a suitable tool to grow the interval faster.