Currently, you can only set the font of a DGN text by using the font number. You can use a DGNStyler or set the igds_font attribute for this.
With FME, you cannot read a mapping between the font number and the font name from the seed file. Moreover, this mapping can vary for every seed file. So there is no easy way to set the font by the font name. My current workaround is to create a new seed file in MicroStation and add some texts, and for the text string value I type the font name. When FME reads this DGN, we can create the mapping between fme_text_string and igds_font. For the actual seed file, I remove the text objects again.
Having the possibility to set the font directly by the font name would be much more convenient.