Good for you for being proactive! That's not what I would prefer or recommend, but that doesn't mean it can't go well and, like you said, the situation was broken, so a fix was warranted. Moisture control means moisture retention from the silicone crystals in the mix, so it will dry less quickly than a non-moisture-control mix. To work with that, I'd try to water gently so the force of the water doesn't compact the soil (described above already.) The less resistance roots have, the more easily they can populate the soil to be more able to use the moisture throughout the pot. I'd also check for dryness before adding more water. The most accurate way to do that, for me, is picking up pots to see how heavy they are (works best with plastic, but with a little practice, also works for clay pots.)
Sending a bucket of good vibes to your beautiful Begonias!
