Actually, since all we need is fixing permissions, simply untarring the tgz packages may do, that is, the post-installation scripts may not be necessary.

Or someone with shell programming knowledge can write a script that lists the contents of the tgz file and the permissions, then apply those permissions to the files on the disk...

I had thought about that, but I cannot remember where slack keeps all the packages used during the install.

It doesn't, so what I suggested is practically no easier than a reinstall.

One last idea, If I make a new partition and do a fresh slackware install there, can I move files from the old slackware partition to the new one?

sure, if you can do it, make another partition, install slackware, boot into your new slackware system, mount the old slackware partition where you have your files, and copy all you want to your new and working slackware partition. after that you can reinstall slackware on the partition it should be, boot the other new installed slackware, copy all files back and do whatever you please with the partition you used to install the "backup slack". Anyway, when you do reinstall Slackware on the partition where you want it to be, i recommend -again- you should first resize your partition and make at least 1 partition for / and another one for /home, so you won't have this problems again when forced to reinstall.