2007 Mazda 6 changing spark plugs and boots

If the smoke is completely white, it is water vapor and can come out of the tailpipe depending on the weather.

If you do not have overheating or coolant losses , ther is nothing to worry about.

If it is slightly bluish or grey, that is oil being burnt. This would happen to most cars when the engine reaches a certain age. If the oil consumption is minor, it is still not time to be worried but you need to keep an eye on the oil level.

On vehicles with the spark plugs go through the valve covers the top seals sometimes leak causing the spark plug chamber fills up with engine oil and in turn when u replace the plugs the first thing that goes into the cylinder is the oil that leaked so yes its going to smoke. Here is what I have done in the past, heat up engine to normal operating temp then run motor at 2500 rpm for 3 minutes and then shut it off, or a long drive on freeway 45 plus miles continuous speeds. If the vehicle never smoked before this will take care of it, the first step may take two times but will work. To fix the problem with the leak, change the valve cover gasket and spark plug chamber seals (they are part of the gasket kit). Hope that helps

Thanks for the additional input