The Scottish Rugby Union has vowed to fund professional teams such as the Borders for the next three years.
But the number nine is focusing purely on the Six Nations.
Cusiter said: "My future and what I do next is a tough issue.
"But my main priority is to play for Scotland and now that I've put myself in that position I want to keep doing it and not do anything to wreck that opportunity.
"You do have to forget about the fact the team might be cut and just get on and play, but it has been hanging there, that uncertainty, and so now it is cleared up a lot of guys will be a lot happier.
"It is also the right decision because two teams are just not enough for competition nor for providing enough opportunities for players.
"If the Borders hadn't existed, I'd probably be sitting on the Edinburgh or Glasgow bench right now."