This page summarizes the general techniques for performing a taxonomic split in Avisys. There are two kinds of split; one where a species is split into entirely new species and the old species no longer exists, and one where part of a species is split into a new species but the old species still exists. We'll use the split of Magnificent Hummingbird into Rivoli's Hummingibird and Talamanca Hummingbird as an example of the first kind of split, and the split of Northern Harrier into Hen Harrier and Northern Harrier as as example of the second kind of split.
Of course, you don't need to do anything at all if you have no sightings of the split species, so we'll assume here that you have sightings of Magnificent Hummingbird and Hen Harrier.
You only need to prepare in advance for the first kind of split, so here we'll only talk about Magnificent Hummingbird. First, rename the species to one of the split species. If you have sightings of both of the split species, never mind that until later; for now just rename the species to the split species for which you have the greatest number of sightings. So, if most or all of your Magnificent Hummingbird sightings are in the United States, or at least no further south than Nicaragua, rename the species to Rivoli's Hummingbird. To rename a species, highlight its name (by clicking on it), click on Edit->Edit Species/Family Name, change the name, and click OK.
For the Northern Harrier/Hen Harrier type of split, there is nothing to prepare in advance.
How to do this is described here.
If you have only seen Rivoli's Hummingbird but not Talamanca, you are done with that split now. Likewise if you have only seen Northern Harrier but not Hen Harrier, you are done with that split. If you have seen both of the split species, you have a little more work to do.
First, find Talamanca Hummingbird and click on the name to highlight it. Then, either press Ctrl-F3, or equivalently click Utilities->Save Species for Edit. Either way, this will bring up a "Saved Species" dialog listing Talamanca Hummingbird. Just click OK here. Then do a List Records of all of your sightings of Rivoli's Hummingbird in the range of Talamanca Hummingbird (Costa Rica or Panama). Change each of these records to Talamanca Hummingibird. To do this, click on the first sighting and then click on Edit, and then on Species. Clicking on Species will bring up the Saved Species dialog that you saw before, and you then click on Talamanca Hummingbird, and then on OK and Finished. You have now changed the species associated with this sighting from Rivoli's Hummingbird to Talamanca Hummingbird. If you have a second sighting, highlight it and press enter, and then choose Yes for the question "Do you want to do mass modifys?", and then simply press enter on each subsequent sighting to perform the rename. Repeat this process for each relevant Place, e.g., both Costa Rica and Panama. The whole process is simpler than it sounds.
For the Hen Harrier type of split, the process is similar. Do a List Records showing all of your Northern Harrier sightings that should be changed to Hen Harrier (e.g., select by Place) and move them all to Hen Harrier using the same procedure as described above.