replacing text (Sorry there was a mistake)

[dgyemen]

Hi,
Sorry if my question is silly, but I have a big text and I would like to reformat it depending on some roles as follow:

$ anything here $ = <b> anything here </b>
#number = [number]
\1\ = <br>

How can I do that, pleaaaaaaase help me.

Thanks.

[SpasePeepole]

dont make 2 posts