Wouldn't worry too much about the torque being out no more than you stated.
Obtaining an absolute and precise torque is more difficult than most people realise..
There is the condition of the threads, the tolerance and finish of the threads, dry or lubricated, bolt head friction against sholder, etc...
And of course, any torque tool is allways a bit out.
The torque is not really the main issue, its the tension in the bolts resulting from the torque applied, and the condition of the threads determines how much of that torque is translated in to bolt tesnion and how much is lost in thread friction.
The only way to have this 99% under controll, is to use a calibrated torque tool, and measure the actual bolt tension obtained with the specific bolts in the specific threads, i.e, to qualify the torquing procedure.
This is only done in critical engineering aplications.
So my point is, for "ordinary" applications, there is usually a good deal of slack involved ,and there is often a relatively good margin of safety designed in.
Of course, some areas are more critical than others.
For instance, if you over-torque big end con-rod bolts, you might deform the big end (usually only elastic deformation) to the extent where the rod and rod bearings bind.
This is however quite noticeable when you try to turn the engine over by hand.
I know someone that did this on a Willy's jeep, they just wrenched upo the big-ends, and the engine could not even be started!
Once they realised what they had done, they just undid the bolts and used a torque wrench and everything was fine!
The only reason to change bolts after torquing, is special applications where bolts are tensioned past the yield limit of the steel. This is not unheard of in many engines, tybically big-end rod bolts. But this is usually mentioned in any maintenance literature relevant to the engine.
But get a torque wrench, and save up for a good one, a good wrench is an investment for life.
I hope this was of some help!
