Odefun: how to modify an equation after a certain time

Hello,

As the title suggests, I would like to modify an equation in a system of differential equations after a specific time has passed. To be more clear: I have a time period of 14 days, so I define

dd = 1:14;
sol = ode23s(@des, [0 dd(end)], y0);

In the

des

system of differential equations, I want to maintain a certain equation until day 7, and then I want to replace it with a different equation from day 7 to 14.

Is it possible to implement such a procedure?