1. Typically, when you paste a new image into an existing image, you should paste it to a new layer. Then, you can select it again easily.
2. Once text is "finalized" it becomes a bitmap and is no longer editable as text. This is another thing you will want to do on a new layer. This way, you can delete it and start again if you make a mistake.
BTW, I edited your post title. Please read the rules: viewtopic.php?f=20&t=3446 before posting again. Welcome to the board.