Hi @Si Hobbs ,
According to my research and testing, you can create Reusable Content in SharePoint.
Steps:
Create Reusable Content:
1.Go to Site content >> Reusable Content List.
2.Choice Reusable HTML.
3.Enter all the column values and save the list item.
Use Reusable Content:
1.Go to target Page >> Edit Page.
2.Click on Page Content field.
3.Click Insert>> Reusable Content
4.Select the reusable content that you want to add and it will be inserted in the field.
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.