[dundee] sed

[Nistur]

I'm sure everyone has at some point heard me herald the beauties of Arch 
Linux and the coolest package manager in the world, pacman, especially 
when combined with ABS. Anyway, I was looking for an RSS ticker and the 
only (first maybe?) one that showed up was GNUsTicker, I later found it 
only had a 0.1 release and then died in 2005. I thought great, if it 
works (screencaps seem to say it does) then I can even start giving back 
to the community and create a PKGBUILD file for the Archlinux User 
Repository and not have to worry too much about maintaining it. However, 
the build system runs in ways that I didn't realise, it makes a fake 
install, well, instead of make install, it basically installs to 
/var/abs/local/$(pkgname)/pkg as the root, rather than / the Makefile 
for GNUsTicker however chmods a file in /usr/libexec/GNUsTicker
Now, the bit I need help with, how on earth do I get it to chmod the 
correct file? I am assuming using sed (hence subject) but sed, to me at 
least looks like someone got angry with a keyboard. I (think I) want a 
sed script to stick a variable at a sensible point in a makefile and 
change a line lower down.
eg.

...
prefix = /usr
...
    chmod a+x $(PYTHONCODEDIR)/gnusapplet.py
...

would hopefully be changed to:

...
prefix = /usr
pkgprefix=`pwd`
...
    chmod a+x $(pkgprefix)$(PYTHONCODEDIR)/gnusapplet.py
...

Thank you to anyone who can help