I think you have to use a WorkspaceRunner.
Extract the 50 contents (listbuilder on the attribute and remove duplicates with a listduplicateremover, explode it) and clla the styler through a WorkspaceRunner.
First make a workspace with the styler and make the blockname a parameter.
If you call this workspace with a workspacerunner, the parameter will become linkabel to a attribute, in your case that would be the contentattribute.
...
Sure you can use a templatefile to refer to (at least) 50 different blocks you would want to use, however you stil can only pick one at a time.
Block name
cannot be reffered to via an attribute, only parameters. (at least not in fme 2014sp3)
If you use valuemapping to map the attributes to blocknames, you still have to select them somehow.
So i think you need to use a workspacerunner, because this allows you to call the dwgStyler with the mapped blocknmames as parameter.
(or you could use python or tcl).
just make sure you are exposing the block name on the writer and FME will take care of the rest, no need for running the same translation 50 times.....
I see it is possible to use an attribute.
Strange, last time i looked it only showed "select block name" and parameter