Regarding how to import additional images on your project, you don’t need to use the same psd. Images that are exported by PhotoshopToSpine can be imported into your skeleton, even if the original PSD is different. You can import additional images to your existing skeleton via Import Data… as you did when you created your skeleton first. After unchecking New project, two options appear and you can use the later one Import into an existing skeleton to import additional images. Also, the Ignore option allows you to import only new images to the skeleton.
Therefore, there is no need to hide other layers when exporting them from PSD. (Although hiding them has the advantage of shortening the export time.)
Regarding how to replace images, there are some ways depending on the type of the attachments. If you want to replace the images of mesh attachments, a dialog will appear if the size has changed since before you replaced it. Please see this section of the User Guide for more information:
Mesh attachments - Spine User Guide: Image resize
If your new images have exactly the same size as the old one, you can replace them by using the Replace option of Import Data as described above.
If your new images have different sizes than the old one, but they are region attachments, you can still import them without corrupting. However, the position of the old images will be inherited and the replaced images will be misaligned from the position on your PSD. Therefore, it is better to delete the region attachments you want to replace before importing new images.
I hope this answers your question.
