I have a couple of modem/routers that came with ISP services that are no longer being used. At the moment I have the current ISP's router running the wireless network and a wired portion to a couple of rooms. In one of those rooms I have a switch to connect all the computers there to the cable coming from the router.
In the other room I have a couple of cables (actually one split into two) but I need at least one additional wired connection there.
Can I convert the existing routers that I have to behave as switches? I don't want these routers to control their own subnet giving IPs to devices connected to it. They should be as transparent to the network as if I just had a few additional wired connections available there.