I can do it by VCDS but don't want to do that as am not always around to revert it back before sending it to w/shop. Do you think Dealer will do this?
It is better to get it done by dealer. No harm in enquiring about this. Actually this Avg FE is of no major use, it doesn't display exact same mileage and is not reliable. My Swift also doesn't have it and it is fine, no difference in feel. If it costs too much, I would say avoid it.
What other modifications you can do, hmm.. nice question. Change to LED lighting, add DRLs or other external lights, upgrade speakers, add amplifier/subwoofer, get LED modifications (underbody/footwell/inside grill, etc.), add HIDs, add bodykit, add spoiler, change wipers to frameless ones, add racing stripes or any other decal, change to OEM
alloys, get stock spec tyres, and best of all, get your car wrapped in some flashy colour! I hope this was a good enough list.