Any and all maintenance must be done IAW some form of approved data. (Are you aware that is in the REG's?)
Now 2a lists who can issue approved data and there is a pecking order. CAsA are on top of that list and within CAsA there is another pecking order like an AD is higher than a AWB on the list - but the REG's are highest on the list.
Next is things like EO's from engineers, then Airframe Manufactures, then Engine Manufactures and finally Component Manufactures.
So if CAsA issues any form of data it is required to be carried out if applicable.
In AWB 20-1 you find this.
"At all times personnel should consult the Instructions for Continuing Airworthiness (ICA) pertaining to the aircraft, engine or spark plug."
So you go to the Aircraft Maintenance Manual to see if they say anything, if not the Engine Manual if not then the component manufacturer for any details.
You clean inspect and gap IAW what ever they say (this is the instruction in the AWB)
Most spark plugs will be covered by inspections and maintenance by a manufacturer, so that part of the AWB is covered.
However the spark plug tester probably will not as it is not a aircraft component, but again CAsA direct you to the equipment manufacturer so you check that if nothing then it is every 12 months.
If a spark plug is required to be tested between 45 -50 psi how can you know what is the pressure if the gauge has not been calibrated.
P.S CAsA have a publication that extends the interval of tool calibrations - but as it is not a AD or in the REG's certain people can not take advantage of it, I think my Spark Plug Tester is at 3 year intervals.