apply a macro only to a set of lines
Use the normal command in Ex mode to execute the macro on multiple/all lines:
Execute the macro stored in register a on lines 5 through 10.
:5,10norm! @a
Execute the macro stored in register a on lines 5 through the end of the file.
:5,$norm! @a
Execute the macro stored in register a on all lines.
:%norm! @a
Execute the macro store in register a on all lines matching pattern.
:g/pattern/norm! @a
To execute the macro on visually selected lines, press V and the j or k until the desired region is selected. Then type :norm! @a and observe that the following input line is shown.
:'<,'>norm! @a
Enter :help normal in vim to read more.