I see what you mean by "branch names" now - if table DIM_ComponentType doesn't work, then you could try DIM_TechType.

Why I can't refit a tug into another? I thought that the only conditions were shipyard size (nature of SY, obv!) and that the ship would not be damaged, but aside that, even if the decision could be stupid (very huge cost) nothing prevented you from refitting any ship into another one?

A shipyard tooled for Class A can only refit (or build) a ship into class B if:

• The cost of new components for class B relative to class A, plus a premium of 20%, plus another premium which is the relative size difference between classes A and B, is less than 20% of the build cost of class A
• There is an additional requirement that the tonnage of class B is less than 20% difference from class A.

These requirements I think were new in C#, at least the second one which prevents silly cases like refitting fighters into battleships. Note that a shipyard tooled for class B can refit from ships of class A regardless of the cost, as long as the size requirement (within 20%) is met.

A common example would be refitting a survey ship from geo to grav sensors, using a shipyard tooled for the geosurvey class. If the survey ship costs, say, 750 BP, and has two survey sensors, then you cannot replace the 2x geo sensors with 2x grav sensors, because the cost of the sensors is 100 BP each and 200 BP x 1.20 (for the extra 20% premium) = 240 BP which is 32% of the survey ship cost, much more than 20%. On the other hand, if the shipyard is tooled for a variant with 1x geo, 1x grav sensor, then you can build or refit to either class because the cost of the NEW components is 100 BP for a single sensor in either case, so the refit cost is 120 BP or merely 16%. On the other-other hand, if the shipyard is tooled for the gravsurvey class then you can refit FROM the geosurvey class without a problem.

For tugs, usually it is not possible to do a refit to a new class in a shipyard tooled for the old class because tugs are almost entirely engines, so upgrading a tug usually means a complete swap of engines which is most of the build cost (refit cost may even exceed 100% of the old variant cost very easily). If you have a shipyard tooled for the new class, then you can refit from the old class without a problem.

Again, note that the examples assume the same or similar size between classes. If the old tug class is 45,000 tons and the new tug class is 90,000 tons, you cannot ever refit from A to B anyways.

Does anyone know if Ship Component type names are scripted in the DB or in the executable? I've edited some names in DIM_ComponentType, yet cannot find how to rename type branch names. Like, my eternal damnation is Geo Sensors, wich I'm mixing up with Grav Sensors every second time; tried to rename Gravitational to Topological in the DB, yet the type branch remains Geological Survey Sensors, wich means I will still mix it up.

Oh, so ...

Ordnance Transfer System: 40 MSP per Hour
Cost 20   Size 500 tons   Crew 20   HTK 1
Materials Required: Duranium  5    Boronide  15   

is for missiles only?

Let's add another senior moment, then 

Why I can't refit a tug into another? I thought that the only conditions were shipyard size (nature of SY, obv!) and that the ship would not be damaged, but aside that, even if the decision could be stupid (very huge cost) nothing prevented you from refitting any ship into another one?

What could explain that my MSP freighter only transfers to Earth MSP at a rate of 10 MSP per hour, and not 40 as per the component it has?

Did you give it an Ordnance Transfer System (transfers Missile Size Points (MSP), not Maintenance Supply Points (MSP), easy to mix up) instead of cargo shuttles?

What could explain that my MSP freighter only transfers to Earth MSP at a rate of 10 MSP per hour, and not 40 as per the component it has?

Does the freighter have cargo shuttles? 

My understanding is that the transfer rates apply only between ships and not ship to colony or colony to ship.

Space stations, the advantage is that they don't use shipyards, the drawback is that they can't be refitted?

Another advantage is that they don't have armor, which makes them lighter and cheaper. (And also, obviously, incredibly fragile in combat.)

You can use shipyards to build stations if you want to, subject to the same size and tooling rules as regular ships.
In fact, I like to build my 25k freight barges and 100k colonist pods in a shipyard--and I can actually build either one with the same yard.

You can also, of course, use such shipyards to refit stations if you like (again subject to the same rules as regular ships).
But no, in the absence of an appropriate yard, a station cannot be refitted.

Another minor drawback of building space stations with surface facilities is that you can't use any component stockpiles to speed up production.

On the Wealth/Trade tab of the Economics window, income and expenditures are broken down by type.

I think I understand that "Tax on Shipping Trade Goods" is the income I receive from the civilian shipping lines when they haul a shipment of trade goods from one colony to another.

But what does "Tax on Exports" represent?
I would have thought that it represented income from shipping to other races (NPRs), but I have only encountered one NPR, and we aren't trading. (They refuse to communicate and I haven't discovered any of their colonies.)
Besides, I was receiving this Tax on Exports income even before I encountered this NPR.

In any given year, I usually make around twice as much on this Export tax as I do on the Trade Goods tax--but it varies.