Multiple styles on same line in Microsoft Word (Protected Document)

[jhopppppp]

I am trying to limit the styles a user can use in a word document. I am doing this by using the "Protect Document" feature.

But after I protect the document, I can no longer apply a style to just a single word without it changing the style for the whole paragraph.

For example if I tried to change the word 'house' to a new style in the sentence below...

There is a house on the hill.

Then the whole sentence would become that style, not just the word house.

Does anyone know how to get around this or what I am doing wrong?

Thanks!