I have found a way to use a centered custom start button image but, you need to install Explorer Patcher and then this fork or Taskbar X. This will get you the Windows 10 taskbar that can act like a Windows 11. With Start 11 it will act as if everything is normal. Once those are installed, turn off all the options that center the taskbar and use Start 11 to center the taskbar. Now you should be able to center your taskbar, Start button, and be able to change the image. Programs like 7+ Taskbar Tweaker will also work now and I would suggest using larger 32x32 taskbar icons option, the default size is 24x24.
(images using the larger 32x32 taskbar icons)


(images using the smaller 24x24 taskbar icons)

Larger 32x32 icons 7+ Taskbar Tweaker:
Right click on system tray icon.
Advanced Options.
(w10_large_icons)
0 - Disabled (24x24)
1 - Enabled (32x32)