in this tutorial i explained how to change icons without using far/xs all the time and it works.
***CUSTOMIZATION and BACKUP OF YOUR PHONE***INSTALLING ICONS WITHOUT FAR/XS++*** - Top Sony Forums

following the same tutorial i tried creating shortcut to layout.xml file so it can be changed in the same way as with icons, but it didnot work properly so don't try it.

to upload new fonts, and for them to be used by the phone, you will have to edit fonts.xml file
don't worry and you only have to change names of the "old" font with the name of the "new" font that you want to use. save the fonts.xml file and upload it with "new" font(s) to the phone, using far/xs.
this is the content of the original FONTS.XML file:
<xml>
<engine cache_size="131072" default="yes">
<font style="sans-serif" weight="normal">/tpa/preset/system/fonts/Sans-Serif_Europe_Reg.ttf</font>
</engine>

<engine cache_size="262144" default="no">
<font style="sans-serif" weight="bold" >/tpa/preset/system/fonts/Sans-Serif_Europe_Bd.ttf</font>
<font style="sans-serif" weight="italic" s01="20" >/tpa/preset/system/fonts/Sans-Serif_Europe_Reg.ttf</font>
<font style="sans-serif" weight="bold-italic" s01="20" >/tpa/preset/system/fonts/Sans-Serif_Europe_Bd.ttf</font>
</engine>
</xml>

so you would change all Sans-Serif_Europe_Bd.ttf with your new font name for example ARIAL.TTF, then save new fonts.xml file and upload it with ARIAL.TTF to the phone with far/xs to this location \tpa\preset\system\fonts