We have a Renumber() action and a RenumberDialog() action. The dialog is 
also accessible via the menu: 
<p>
edit/change multiple objects/renumber symbols.
<p>
The dialog shows and explains all arguments to the Renumber() action. The 
action takes all selected symbols (or all symbols on the sheet) and starts 
renumbering them from the specified base number (1 by default). It tries 
to assign numbers per prefix (i.e. counting separately for R's, C's, U's, 
and whatever non-numeric name prefixes you used) but it also makes sure it 
does not assign a name that is already in use on the sheet by a symbol you 
are not renaming.
<p>
There is a sort argument that tells how symbols-to-be-renumbered should be 
sorted before renumbering. This affects how the numbering goes, 
e.g. left-to-right or right-to-left.
<p>
The typical use cases:
<p>
<ul>
<li> you are lazy, and just renumber everything on your sheet, e.g. once it's 
already too messy

<li> your drawing contains sections; you select everything within a section 
and renumber them with a base of 100, so you get R100, R101, R102, etc; 
then you renumber another section starting from 200, etc.
</ul>

<p>
Unlike <a href="../fix_unnamed">"fix unnamed"</a> feature, the renumber
plugin really renames your symbols on the drawing (in the concrete model).
<p>
Note: at the moment the action works on sheet basis. Later we may extend 
this to project basis (so that naming collisions are avoided not only 
within the sheet, but within the project). We may also introduce more 
sorting methods, those are cheap to implement.
<p>
Note: this is all in a plugin, and is not part of the official cschem 
specification. I consider this an optional feature; some users may want to 
have it differently. They can implement their idea in an user script. They 
can even disable the renumber plugin and implement an user script with the 
same actions to replace it!