is there a way to change the grip size

[Gold-]

is there a way to change the grip size from G5 to G4 without changing or change a minor bit of the bp of the racket itself ?

[Danstevens]

Well, because you want to add size, you're going to need to add a little bit of mass. If you think about it, you can't make the grip bigger out of nothing.

You can increase the grip size with either a heatshrink sleeve or adding an extra grip/overgrip. The heatshrink sleeve is preferable as adding more grips makes the handle "mushier". However, as stated above, these will add weight (albeit that IIRC, heatshrinks add barely any weight). You have two realistic options to neutralise this weight gain if you want to. Firstly, there is the option to do nothing at all. This will leave you with a slightly heavier than stock racket with a more headlight balance. The actual swingweight will remain the same. The second option is to work out how much lead/other weight product you would need to add to the head of the racket in order to obtain the same balance. This would leave you with a racket with the same balance as when you started but with a higher static weight and swingweight.

If you're going to do this, I would recommend that you find somewhere to buy one of those heatshrink sleeves to increase your grip size. It's perhaps not quite as easy as just wrapping another grip on top of your existing one but it will give you much better results.