Both Czech Smrz and Australian Aitchison finished the 2012 season with the team after leaving World Superbikes.
Smrz developed through the 125 and 250cc World Championship before spending five-and a-half seasons in WSBK.
"I am very happy to re-sign with Splitlath Redmond for 2013. I had the chance to make the last races with the squad this season and really enjoyed the BSB championship and working with all the guys," the 29-year-old said.
“We did three rounds together so now we know what needs to be improved to give me and Mark the best to be on top, but I know this team is able to get us there.
“I am working hard on my physical condition and the team is working hard to get my Aprilia as fast as possible and put together strong people working for me. I can't wait to be back on my bike again.”
Aitchison completed four rounds last season, one more than Smrz, after leaving the Grillini Progea Superbike team.
"I'm very excited for the opportunity to continue on with the Splitlath Redmond team for 2013,” Aitchison said.
“Ever since I joined the team I have felt like a part their family. The latter half of 2012 was quite difficult for me, coming back from injury and attempting to regain some confidence, but I've been very fortunate to have such a supportive team around me.
“With their patience I was able to come back almost fully fit and build some momentum for next season. We have some big targets for next year, so I'm really looking forward working with my crew and Kuba to put both these Splitlath Redmond Aprilias at the front.”