If done right you should not have any problems. I would just drain from the drain plug, and measure it using an empty oil bottle. And then add the new stuff. Do it at the same time you do engine oil. Its 2 quarts on a Gen 1. Basically you did that a few times sorta when you did the seals. Do it slowly like that and all will be good. Having cleaner and newer additives will make it happier. I would wait a few changes before dropping the pan. I did a pan drop on a high mileage Subaru one time, it was a waste of time, I didn't use the new screen and had to mess with the pan gasket sealant etc. inside it looked new. And I know the dirty fluid had at least 150,000 on it. I now believe in changing the trans fluid at every engine change.