open file1 for input
open file2 for output using >> so it appends
.marker1.
read a single line as variables $1, $2, ...
use switch/case to select the field(s) you want to fix or alter
change it(them) for that line of input (with case selecting fields you want to alter in order)
print to (output) file2 the variables $1,$2...
check if endof input file
if not goto the next line of the input file
loop to .marker1.
if eof input file
add a print "\n"; to the output file (you usually need it)
and close both input file and output file