Thanks for contacting regarding Metro studio and its really glad to hear it from you :-) At present you can't have the combined icons by your own. We already have the collection of combination icons, So please provide us the icons details and we can work on it and can provide you the needed icon.
And thanks for your valuable request. Hopefully, we may consider this feature in future. Keep enjoy the Metro studio :-) :-)
Please feel free to contact us with any other request/queries.