Identical content with variables on many pages editable from one template ?

Hi everyone, i’am fresh with wordpress but i’am in love in WordPress CMS. I have a site where i need to create 500 pages with identical content but with diffrent keywords for example:

Page 1 Content:

Lorem Ipsum is simply dummy text of the printing and typesetting industry for a Blue Book. Lorem Ipsum has been the industry’s standard dummy text ever since the 1500s for a Blue Book, when an unknown printer took a galley of type and scrambled it to make a type for a Blue Book.

Page 2 Content:

Lorem Ipsum is simply dummy text of the printing and typesetting industry for a Red Book. Lorem Ipsum has been the industry’s standard dummy text ever since the 1500s for a Red Book, when an unknown printer took a galley of type and scrambled it to make a type for a Red Book.

and 498 more pages like that… its no problem for me do this, i can spend day or two and work will be done but what when i for example will need to add extra lines or edit line of text in all pages ? then i will be forced to edit 500 pages and this is very painful ?? i’have read about custom page types, custom posts types, custom extra fields and i can’t get this working so i have one “mother content template” with i can edit from one place and my changes in all pages will be done in seconds but still remaning my variables like Red Book, Blue Book etc.

Can somebody can help me with this ? maby plugin that i didint found, maby combination of two plugins ?

Thank You All and very sory for my bad English but i’am still learning ??