Add Style after adding plug-in.. Plug-in not working

[FCDobbs]

I have been asked to help some people with their site.
These are new owners of the site, and they wish to make some changes.

First, the site has about 10 "plug-ins" added, and most are working fine.
Second, the site has about 5 different Styles.

So these new owners didn't like most of the styles, and they deleted some of them.
Then they asked me to install 3 "nicer" ones.
I did... the installation went fine.

But now, some of the Plug-ins don't appear/work with these new Styles.

So....

How to (easily) make the Plug-ins work with the new Styles?
I have examined the code changes to make the Plug-ins work.... it will be a very onerous
task to make these changes MANUALLY to all the templates of the new Styles.
Not only that, I am not sure just where to put/make these changes within the Style templates.

Could I re-install the Plug-ins, and would that do the trick ?

Or do I have to manually make all the changes ? (and hope that I don't screw up)

Thanks