To start you will want to download iHex from the App Store. Here is a link for it,
You'll need to know what your CPU is shown as in About this Mac before you start. For mine it was shown as Intel Xeon Quad-Core.
Once that's installed open Finder and navigate to, Copy the AppleSystemInfo file to your Desktop and make an extra copy in the Documents to be sure. Now rename the original file inside the framework to AppleSystemInfoBackup.
Once you've done that open iHex and drag the AppleSystemInfo file onto the iHex window. From here you can expand the window so it's easier to read.
Now in the menu bar choose, Edit > Find > Find and change the type to Text and search for CPU. Your screen should look something like this,
Now find the Intel CPU string that you system is showing and note how many characters long it is. This includes the spaces. For my example Intel Xeon is 10 long was changed to AMD FX4300 which is also 10.
Once you've done that from the Menu bar choose File > Save. A popup may appear, just click on Save.
Now you need to open up Terminal and enter this command,
sudo codesign -f -s - ~/Desktop/AppleSystemInfo
Enter your password and you should see "replacing existing signature". Once that's done put the modified file back inside the Framework and open up About this Mac. You should now see your changes
Installed Operating Systems: Mojave 10.14.3 - Windows 10 Pro (Insider)
CPU: Ryzen 5 2400G Motherboard: GIGABYTE GA-AB350-Gaming 3 RAM: 8GB DDR4 Graphics: ASUS ROG Strix RX560
HDD: Crucial MX500 250GB - 2TB Seagate - 640GB WDC - 500GB WDC LAN: RTL8111 Sound: HDMI
Other: USB Bluetooth - USB Wireless Mouse and Keyboard Bootloader: Clover