Need help for Nick Gammon Bootloader

Hello! Greetings!

While searching for arduino Bootloader I came across Nick Gammon Bootloader, This is the link
https://www.gammon.com.au/bootloader

Really Cool and AWESOME thing!!!

Then I thought that I should make my own board based on 328 or 2560 may be and attach some tactile switches to it and couple of zif sockets so that I can make all in one arduino bootloader programmer. For this I really wish I could combine the codes written by Nick Gammon and by pressing the tactile switches that I connect t it I will be initiating different options or the different codes. So my question is, Is it possible to combine all these codes in a single chip at once? and then use different keys for different code to run? If so, how should I do it? I tried to read those examples but I find it pretty much complicated like where to begin with the integration and likewise, moreover I can see couple of other files added then how can I combine those into one single code? I don't know if this can be made possible or not. May be my question is just lil amateur. Any suggestions what can be done?

Thanks in advance