import re
elements = ['Radio0', 'Tether0', 'Serial0/0', 'Eth0/0', 'Eth0/1', 'Eth1/0',
    'Eth1/1', 'vlanX', 'modem0', 'modem1', 'modem2', 'modem3', 'modem6']
repl = 'XYZ'
for i in range(len(repl)):
    elements = [re.sub('[0-9]', repl[i], element, 1) for element in elements]
result = set(elements)
Transform list with regex