I wouldnt worry about tweaking the rules in any way you see fit, especially if you are playing solo.
Most groups of Mordheim players have their own 'house' rules.
So long as all the players know what the differences are, and they all agree, you should be fine.
One of the rules that we changed was the rules for shields, as they are so poor in the original form.
When combined with a 'hand weapon' (sword, axe, spear, club, etc) they receive an extra +1 to the save, as in the more recent versions of Warhammer.
They also receive a 6+ 'Invulnerable' save against any attack, as they should always have a chance of saving you in some way. (A piece of wood and metal that is, effectively, the size of a small door should always give you some protection!)
Before we did this it was almost pointless taking a shield, it was much more effective to take a second weapon for the extra attack. Now shields are becoming a much more commonplace piece of kit, as they should be and have been for long periods of warfare.
Tweak away, mate. Tweak away....