Yes, basically the seal just presses on. Remove it gently at first until you get the idea of how it fits, then you will have the idea. Putting it back on is simply a matter of pushing it back on.
These sorts of hatches notoriously rust away on this lip which allows water in.
If so, only option can be welding or replacement if you can find a better one.
New seals are almost impossible to find, but you could try Toyhead in the US.
They have a good reputation amongst the Celica guys here in Australia. Many get their seals from him. Something about the genuine seals having a lip to retain the headlining, which apparently Toyhead stock.
BUT, if the lip is rusted away, the seal won't fix your leak.