If you wish to create text blocks that can be imported into several activities, you should look into creating HTML blocks. If you use HTML blocks in course templates instead of normal text blocks, all courses that are based on the template will be updated.
Create an HTML block
Go to the Library and choose “Materials”
Click “Add materials” and choose “Text/HTML blocks”
Name your HTML block and add your text
Add the HTML to any projects you like
All done!