You're looking to infuse Alton Brown's eggnog with flavors reminiscent of horchata and rompope. This involves incorporating ingredients like ground rice, ground almonds, cinnamon stick, clove, and star anise. The primary concern is how these additions will interact with the traditional eggnog aging process. Generally, most spices and flavorings can be aged with eggnog to allow flavors to meld. However, ingredients that can break down or become overly bitter with extended aging might be best added later. Whole spices like cinnamon sticks, cloves, and star anise are typically added during the aging process to infuse their oils. Ground rice and almonds, however, could potentially alter the texture and clarity of the eggnog over a six-month period. They might also contribute to a slightly gritty or cloudy consistency if not fully integrated or strained out. Some of these ingredients, particularly delicate nuts or starches, might be better introduced closer to serving. This approach ensures their fresh flavor and prevents them from becoming overpowering or degrading. You could experiment by aging a portion of the eggnog with the whole spices and then adding the ground rice and almonds to a separate batch for a shorter aging period. Alternatively, consider adding the ground ingredients in the last month or few weeks of aging. This would allow some infusion without the risk of prolonged degradation. Testing small batches with different addition timings would be the most reliable way to determine the optimal method.