Changing the Indentation of existing source lines in /free when adding a new If/for etc in between

Is there are trick to changing the existing indentation you have for a block of code when you are adding a new if/for at the top of the block and the endif/endfor at the bottom of the block?

Say you have

if b = 1;
if c = 2;
if d = 3;
blah = blahblah;
endif;
endif;
endif;

You need to modify this to put if a = 0 at the top of the block;

if a = 0; <----- (How to indent all the existing code a couple of spaces?)
if b = 1;
if c = 2;
if d = 3;
blah = blahblah;
endif;
endif;
endif;
endif; <-------- (New endif)

Thanks
Andy