Modifying iOS/Android Interface Elements - Is It Difficult?

Question

Android

I draw the interface design of a mobile game for ios/android. Of course, I want to move away from the guidelines, for example:
- make a custom menu bar that contains a burger or a back button (and other navigation buttons on various screens), a screen title - change the icons and font of the title;
- customize input fields, drop-down lists, buttons, checkboxes, etc.
- use a non-standard grid and padding from the edges of the screen
- customize other components (tab-bar, bottom navigation bar, etc.) - fonts, text layout, icons and other design.
I don't know how exactly to formulate the question. So don't kick your feet. I ask how the design is, not the developer. The question may sound like this:
- Will it be difficult for developers to implement custom "designer" components?
- Will it greatly delay the development?
- Is it justified to use custom component design?
- How much less productive will custom component design be compared to native?
- In general, what is your attitude towards custom design of components in mobile interfaces?

Answer 1

It is justified in games, but usually everything is not drawn on standard components, in ordinary applications it is not justified, since it is necessary to adhere to Google's guidelines so that applications look more or less the same.

Answer 2

Write in Unity3D: everything can be done there as the designer drew.
Better, immediately find a ready-made Asset (GUI) for the desired style and carefully adjust / combine the design.