From an ESP32 perspective, replacing .csv files with .yaml files for rarely loaded configuration is not costly in terms of performance or memory, as long as:

The YAML files are not excessively large.
You use a lightweight YAML parser (such as arduino-yaml or a minimal C++ YAML parser).
Configuration is only loaded occasionally (not in a tight loop).
Pros of YAML:

More readable and maintainable for complex or nested data.
Supports comments and richer data structures.
Cons:

Slightly more code and memory required for parsing compared to simple CSV.
Fewer lightweight YAML parsers available for microcontrollers than CSV/token-based parsing.
Summary:
If your configuration is not huge and is only loaded at startup or on demand, switching to YAML is reasonable and will not significantly impact ESP32 performance or memory usage. Just choose a minimal YAML parser suitable for embedded systems.

So format will be

```yaml
Name: "Loco name"
Image: "File name"
Vmax: <speed>
Functions:
  F0:
  F1: 
  F2: 
...
  F28:
Decoder:
  Brand:
```
