Everyone's talking about choke tubes and nobody's answering the question.
Yes, you can buy different shot cups that will have a different pattern at different ranges. The old Federal shotcups had very shallow side cuts and held the pattern tighter (i.e. the shot cup stayed with the shot longer and kept the shot together longer so that your pattern was tighter), Win AA Field shotcups had very deep side cuts and spread the pattern very well fairly quickly, and there were even shot cups called spreader cups that had a post in the middle of the cup to spread the load out very quickly (but they often blew the pattern for anything beyond 25 yds).
From the sounds of what you are talking about, you might want to talk to a knowledgeable smith about cutting a longer forcing cone, this was used to reduce recoil and tighten patterns in fixed choke guns. Just be careful who you choose to do the work, because once you recut the forcing cone, there is no going back!