Insert character x at...

Hi all, I'm needing some help creating a command line that's hopefully simple.

I'd like to use a sed command in a batch file to do the following on a fixed format input file:

For every line in input file that begins with '0530' (in first 4 characters on line), insert 'x' at position/column 32 on same line, then output the whole file to a newfile.

Optionally, if its possible to delete one character (a blank space) on same line at position 34, that would be helpful as well, to preserve formatting.

Any/all help is greatly appreciated.

Thanks