You can do something similar to this recent answer: https://stackoverflow.com/a/22238813/3130080
For example,
:%s/\%6c/x/
will insert "x" before the 6'th character in each line, and
:1,2s/\%>1c\%<4c.//g
will delete characters 2 and 3 in lines 1 and 2.
:help /\%c