Vim search and replace from current location to end of file

Instead of searching and replacing the entire file with...

:s/old/new/g

Try inserting ".," just after the colon. This means "from current position to end of file".

:.,s/old/new/g

The comma actually specifies a range to make the substitution, from left and right of comma. For example...

:5,10s/old/new/g

...makes the substitutions on lines 5 through 10.