How to change the keyboard for alphanumeric password on lock screen on iPod
Good morning! report it to Apple support 
Request them to investigate, ask them to inform you and also post "how to" on their website as well

Note: Usually Apple or other smartphones makes only post the most common situations or most common inquiry's answers 

For those more specific questions, one has to ask them to investigate and post it 
If there is an Apple support agent or technical support person that knows how to use his or her resources and is willing to investigate on it for more than 5 minutes, they may be able to get you an answer

Thanks!