U can do it at any SC. Ur car still relatively new...have u tried other swift before? Maybe ur level of performance acceptance has changed....Irridium plugs and fully syn. oil are worth to try also....Next will be the performance Monster air filter when it is due to change
However, i noticed that the exhaust conversation (header, decat, midbox and S-muffler) does not provide satisfactory result but higher FC...happy modding

Ok...how much does the SC charge and what do I tell them...fasten the accelerator cable?

No, have not tried other Swift before. From the very beginning I got the car, I noticed performance is lethargic compared to other 1.5s like Vios or City. The gearbox is really unresponsive, like sleepy only. It just feels reluctant to downshift when u press the pedal, that's why the performance is poor.
Tho I also drive a VW GTI, but I don't compare that against the Swift coz no comparison at all. Just that when compared to other 1.5, Swift performance is really weak. Always kena overtaken by other cars, especially those Myvis...haha.

I have a K&N drop-in filter installed. Still, after a while using it and getting used to it, like no difference. Maybe follow your advice and get the SC to so call tighten the accelerator cable.