We refer in our descriptions to the technical condition of a device. A quick explanation for you to have a better understanding.
Maintenance: this refers to the process of opening a device, inspecting, measuring and following the maintenance steps recommended in the service manual of this device. For an amplifier, it usually consists of an internal and external cleaning with non-toxic products, visual inspection of the components for leaks and aged soldering contacts, deoxydation, and adjustment of the bias currents. For a speaker, internal inspection of components and contacts, condition of the crossover filters and the absorbing foam, free movement of coil based cones, impedance check.
Restoration: for a device, like an amplifier, this refers to the replacement of components with their original value counterparts. Typically you will read about a "recapped" amplifier, with means some of the capacitors were changed by the same value counterparts. Old chemical capacitors may leak or be out of value with age; changing them brings back the original condition of the amplifier. This job may mean changing two or perhaps twenty capacitors, depending on the work needed.
Some other parts like transistors may be involved if they are corroded. It is good practice not to change working parts if they are still measured at their original value, not to alter the sound of the device. For a turntable, changing the belt (if belt driven) and the stylus is common practice, the suspension sometimes need new rubber feet.
For speakers, the cones are suspended by foam rings that perish with time and greatly degrade the sound. Changing them for new suspensions bring back the speaker to the original condition. For dome tweeters, they may have burn or lack volume, the diaphragm is then replaced. All speaker operations are always done by pair, the left and the right, for sound balance. Finally, the crossovers do also use capacitors, that may be out of range. Changing them by contemporary counterparts of the same value will improve the sounding clarity.
Past all those technical considerations, restoration may also be cosmetic: veneer, speaker cone nurturing, new speaker grilles, amplifier cabinets…
Modding: modding means modifying parts, for comfort or for the sound performance. The most basic comfort "modification" on a loudspeaker is to change the connectors or screws to a more robust and reliable banana plug set. This does not alter the sound, so it is generally just mentioned in the description.
Futher in modding, sometimes we may have to replace a component because the original value does not exist, or because the modification is proven to bring a clear improvement. Typically, a slightly stronger capacitor may bring clarity and punch. Modding should always be limited and based on proven benefit, we always prioritize the originality of the specs, hence you will see seldom modified items on Vintage Note.
Do not confuse the way we consider modding with swapping parts for contemporary components. Often seen on second hand speakers, changing the woofers or tweeters by contemporary counterparts is not respecting the original sound of the product. It is a matter of taste, but we do not present such "hybrid" items.