You could keep a single soulmeld bound forever if you wanted to. However, you can't shape the soulmelds one at a time
A meldshaper must shape all his chosen soulmelds at the
same time. He cannot leave a soulmeld slot unfilled in order
to shape it later.
You must have access to all the soulmelds you want at the same time. Then you shape them all at the same time. Any soulmeld you want bound to a chakra is bound at the exact same time. In effect, you have to clear out all your old soulmelds to put on a new one.
As for swapping out Shape Soulmeld as your chameleon bonus for another and keeping the soulmeld you chose; assuming you keep it bound forever, it could be argued you can keep it for the duration. Reasonably, probably not. It really is up to your DM.