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I would do the following:
- create a mask of your ROIs for your original classification image (Basic Tools ->Masking->Build Mask). Import the ROI under Options and choose 'Selected areas off'. This should create a mask of 0s where your ROIs are and 1's for the rest of the image.
- Apply the mask to the original classification image (Basic Tools ->Masking->Apply Mask). Select the classification image and mask on input. Here you can set the background (0s) to whatever value you want. If you want the ROIs to go to an existing class, then choose that class number (1,2,3...n). If you want it to go to a new class, then set its number 1 larger than the maximum number of classes. For example, if I have an image with 7 classes, I would set my masked area to a value of 8 to make it a new class.
- if you make your masked area a new class, you will need to edit the header to set up the number of classes. Go to File ->Edit ENVI Header ->Edit Attributes ->Classification Info. It will ask you how many classes you want. Enter the new number of classes plus 1 for the 'Unclassified' class. So in my example above, I originally had 7 classes (plus unclassified). So I would enter 9 as my number of classes. In the Class Color Map Editing tool, you can edit the class names or colors as desired.
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