All the better :)

Categories will be replaced by tags in Horde 4.

Currently, there is no feature that allows renaming a category. The 
only way to do a rename is creating a new category, edit every item 
you want to have the "new" category and delete the old one afterwards.

/* Of course, I used an SQL-Query to do this, but not everyone does 
have admin access to the database Horde is using. */



I think this reflects a design that is imho very poor: Categories seem 
not to be referenced with an (guaranteed) unique identifier but with 
their name. If you delete a category, existing items are not changed 
but are identified as dirty at runtime. In other words, you leave 
inconsistent data.



The problem I mentioned can be solved even with this design: If a 
category's name is changed (provided there is no conflict), identify 
all references and change the value (one query on the item table of 
each application using categories).



I couldn't even find out where categories are stored in the database 
currently. I would prefer a separate, application independent table 
for them, containing ID, name and color (maybe a delete flag if you 
want to preserve current behaviour on delete. Would prefer solution 
using SQL that sets references to default value on delete). Then, 
renaming a category can be done in constant time.



/* Additionally, one may think about features such as 
merging/splitting categories or category hierarchy. Those might come 
in handy. */