Innovative multi band (MB) sliceable bandwidth/bitrate variable transceivers (S-BVTs) are proposed for future adoption in next-generation optical networks towards targeting the expected capacity scaling driven by the increasing traffic demand and emergence of new 6G services and applications with stringent requirements. To provide enhanced bandwidth/capacity and energy efficiency to support the envisioned growing demand, the use of MB technology is proposed and experimentally assessed up to 75 km of standard single mode fiber (SSMF) considering programmable MB S-BVTs. We demonstrate an aggregated capacity of 132.2 Gb/s exploiting S+Cbands and scalability towards enabling multi-Tb/s transmission within the metro/aggregation network segment. The sliceability of the MB S-BVT is demonstrated considering joint MB transmission (S+C) up to 2-hops network path of 75 km and an additional span of 50 km of SSMF for the C-band contribution. Different configurations based on single side band (SSB) and double side band (DSB) modulation and amplification technologies have been evaluated according to the particular scenario and band of operation. Finally, the programmability of the presented MB transceiver is also assessed as a key capability to promote network automation and flexibility. On this regard, a software-defined networking (SDN) agent based on open data model, such as OpenConfig, is implemented and validated to suitably reconfigure the transceiver according to the network requirements/demand. Key operational transceiver mode capabilities and configuration constraints, for the agent's implementation, are identified towards supporting MB transmission within future optical networks.