[EdKiefer]

while most tuner type tune/reflash does improve efficiency , its partly done by leaning A/F at high loads and increasing ignition timing , its tuned for 91+ fuels .

Now for eco uses you want to remap part throttle area, but this area of load is closed loop modes and is mapped to the A/F of O2 sensor . So you have to somehow adjust this or any changes will be reverted, learned back to the ECU O2 closed loop values, which are for most vehicles around 14.7 .

So depending on the unit and type of hardware (reflash, daughter board, piggyback ,etc) this will be a go or no go depending if you can adjust closed loop modes .