Combining recordings from different rooms
Combining sample libraries or recordings that have been recorded in different rooms with different ambiences in one piece is usually not that much of a problem as some people think or make believe. Especially in more tutti situations it is very tricky to hear the different rooms anymore (unless you’re combining pratically dry samples with samples that are very wet from the beginning, in this case you might want to use a reverb on the dry ones). If you’re combining room sounds in a more exposed way (e.g. solistic lines) it becomes a little more tricky but helps to add the same reverb to all signals (and adjust according to how wet the individual signals were) which is also something that helps in the tutti situation to give it a bit more of a uniform sound. Be aware that that argument of “You should not combine different rooms because it might sound problematic” is mainly an argument that sample developers like to use in order to have a selling point to make you purchase a whole line of samples that have been recorded in the same room. In reality, I haven’t experienced many problems from combining different libraries.