Can I change the code through Library objects but not the text in it?

My first post here guys (:

I have a problem which is that while I constantly need to tweak the design of a website, the contents will not change. Also, because I have many pages with page-specific contents but similar design formatting.

therefore to put it simply,

I have a few pages

Page 1:
<b><i> abc </i></b>

Page 2:
<b><i> def </i></b>

Page3:
<b><i> ghi </i></b>

I want to change the <b><i> and the </i></b> but I do not want to affect the abc, def or ghi.

I have tried experimenting with libraries objects, ie <b><i> as one library object and changing it, but it gets too complex as I have to close it up with another </i></b> library object.

So here I am asking you guys if there's any way to simplify this process.

Thanks guys!