Consolidating subnets - Is it possible to have two default gateways?

Hopefully an easy question. Looking to consolidate two /24 networks into a /23.

Due to lack of access to some existing devices it would be useful if we could retain both existing default gateways e.g 1.1.1.254 and 1.1.2.254 so we don't need to reconfigure the devices. Is this possible and recommended?

Also any downside to not changing the mask on existing devices as long as they don't need to communicate with devices on the other /24 range?

Hopefully a simple question but wanted to double check. Thanks as always.