Change resistor "properties" from SMT to feed-thru?

I assume I need to activate a "hardware library ".
Where do I start ?

I don’t understand to your question, but try to do according to documentation: LibrePCB User Manual

I agree, all the resistor “symbols” in the Passive > Resistors library appear to be SMD chip components. There are no plain regular carbon film thru-hole devices, and all the schematic symbols are simple rectangles instead of the global standard of a “zig-zagged” line.

For TH resistors, you can use my library RoyalOhm resistors - contents carbon film fixed resistors 1/4W, but it is a testing library yet.

Global standard - We know two standards EU and US for electronic graphical symbol. Are based on the standards IEEE315 / IEC60617 resp.
LibrePCB library can contains boths symbols. Which symbol you will use, depends on your selection → In schematic editor use “Add component” and select your preffered norms: