It'll be fine long as you don't add any fertilizers on top of what're already in there. If you truly got ALL the slow release pellets/balls out, still don't add any fertilizers until the seedling has several sets of leaves or is a few inches tall, or both. Don't adjust the PH: I never have and I've never had a plant of any species go weird on me like some of the plants I see on here.
You can add up to 50% perlite (as in 1:1 Perlite:Soil-mix), though owing to how stupidly overpriced perlite generally is, I usually go about 1:2 or even 1:3 if I'm running low. But a 1:1 mix will make for very happy, healthy roots.