Replace element in a nested list

[nagymusic]

I’m writing to ask if you could help me with a short Python example. Here’s a list of the list of strings:

my_string = [[89, 111, 117, 32], [104, 97, 118, 101, 32], [109, 97, 100, 101, 32], [109, 121, 32], [115, 111, 117, 108, 46]]

Could you suggest how to implement this into a statement that would enable one to replace all values less than a certain value by None (32, 46 => None), and then subtract the rest of the lists by another value? Something like:

if number < 65: q = None
else q = number - 12

I tried implementing this statement but with no luck:

for i in my_string:
    if i < 65:
        i == None

I imagine it must have to do to something with the fact that I’m using a nested list of strings, which I need to preserve.

Thank you for your time!