Office Guy's solution is the definitely the quickest and safest way, especially as you are about to sign-off on the project.
At or about line 31 in each of these files is the beginning of the 'ToolbarSets' section: FCKConfig.ToolbarSets["Custom"]. The only thing to be careful of here is that when you remove one or more of the buttons, that you leave the remaining items' punctuation intact.]
I'm not sure why you are having a problem re-entering the HTMLEditor interface, though.
If your editor instances are in your PowerCMS site, then you would open up either contents_insert.php or contents_update.php page, and re-enter the Editor interface by clicking on the HTML Editor instance (in 'Design View') to select it. It might already be selected, and clicking would then de-select it. In that case, just click once more.
Once selected, you should see - in the Properties Panel/Inspector at the bottom of the window - 'HTML Editor [Edit]' (see attached image)
Clicking 'Edit' should open the HTML Editor UI.
NOTE: If your PowerCMS folders and files are all in the root directory and NOT in their own folder in the root directory (i.e. 'CMS', 'PowerCMS' or 'CMS102'), then re-entering the HTML Editor UI and making changes is fine, go ahead. HOWEVER, if your PowerCMS files and Folders - including the HTML Editor folder - are in their own folder within the root folder of your site, then making changes through the Editor UI will just create a new HTML Editor folder in the root directory of your site and really confuse matters.
How to get round this:
Go to 'Manage your Sites' in the DreamWeaver menu ('Sites'). Select your site and create a duplicate. Click 'Edit' to edit your duplicate site. Change the local and testing server paths for Local Root Folder, Testing Server Folder and (Testing Server) URL Prefix to the folder that contains the PowerCMS files and folders. For Instance, all references to these folders in my site that are currently: C:\Inetpub\wwwroot\Pictuality\ would become C:\Inetpub\wwwroot\Pictuality\CMS\.
In the Local Info screen for 'Site Name' just add the suffix 'CMS' to your site name, and save the site definition. Now (and whenever you want to), using this site definition, you can re-enter the HTML Editor UI and make changes without HTML Editor creating a new directory and big problems.