Yeah, that can be a bit annoying. The cleanest way to do it (if you don't mind editing the AI file a little), is to 'comment out' the driver whose car you intend to drive from the xml file.
So for example, if you want to replace Blundell at McLaren add "<!--" before the <driver livery_name... > tag, and "-->" after the </driver> tag), like this:
<!--
<driver livery_name="McLaren-Mercedes - M. Blundell #7">
<name>Mark Blundell</name>
<country>GBR</country>
<race_skill>0.77</race_skill>
<qualifying_skill>0.80</qualifying_skill>
<aggression>0.71</aggression>
<defending>0.51</defending>
<stamina>0.69</stamina>
<consistency>0.81</consistency>
<start_reactions>0.85</start_reactions>
<wet_skill>0.74</wet_skill>
<tyre_management>0.78</tyre_management>
<blue_flag_conceding>0.91</blue_flag_conceding>
<weather_tyre_changes>0.72</weather_tyre_changes>
<avoidance_of_mistakes>0.49</avoidance_of_mistakes>
<avoidance_of_forced_mistakes>0.33</avoidance_of_forced_mistakes>
<vehicle_reliability>0.52</vehicle_reliability>
</driver>
-->
Anything between the <!-- and --> is ignored, so Blundell will not appear in game. Or, you could simply delete the entire Mark Blundell chunk of XML above, which will have the same effect - but maybe keep a backup of the original.
Hope that makes sense. Hopefully Reiza will come up with a proper solution for this issue in time.
