What is the default Faith Conversion Speed game rule in CK3?

Default: Conversion speed is unchanged. (patch 1.20.1.2)

Does changing the Faith Conversion Speed rule disable achievements?

Yes for “Faster” and “Significantly Faster”: the file gives them the flag blocks_achievements. The other settings keep achievements on.

Game rule · Tweaks · Historicity · Faith

Faith Conversion Speed

Default
Faster ✕
Significantly Faster ✕
Significantly Slower
Slower

Faith Conversion Speed is a game rule in Crusader Kings III (Tweaks, Historicity and Faith) with 5 settings: Default (the default), Faster, Significantly Faster, Significantly Slower and Slower. “Faster” and “Significantly Faster” disable achievements. Patch 1.20.1.2, from game/common/game_rules/00_game_rules.txt.

This section as JSON: /raw/game-rules.json

Quick answers (2)

What is the default Faith Conversion Speed game rule in CK3?: Default: Conversion speed is unchanged. (patch 1.20.1.2)
Does changing the Faith Conversion Speed rule disable achievements?: Yes for “Faster” and “Significantly Faster”: the file gives them the flag blocks_achievements. The other settings keep achievements on.

5 settings

Default
Default
Conversion speed is unchanged.
default_faith_conversion_speed
Faster
Disables achievements
The speed is increased, making conversion take roughly half of the time.
The script checks it once, in 1 place
Script values 1
- court_chaplain_conversion_factors
Every has_game_rule = faster_faith_conversion_speed in game/common and game/events, by the top-level object it sits in.
faster_faith_conversion_speed
Significantly Faster
Disables achievements
The speed is significantly increased, making conversion take roughly a quarter of the time.
The script checks it once, in 1 place
Script values 1
- court_chaplain_conversion_factors
Every has_game_rule = significantly_faster_faith_conversion_speed in game/common and game/events, by the top-level object it sits in.
significantly_faster_faith_conversion_speed
Significantly Slower
The speed is significantly reduced, making conversion take roughly four times longer.
The script checks it once, in 1 place
Script values 1
- court_chaplain_conversion_factors
Every has_game_rule = significantly_slower_faith_conversion_speed in game/common and game/events, by the top-level object it sits in.
significantly_slower_faith_conversion_speed
Slower
The speed is reduced, making conversion take roughly twice the time.
The script checks it once, in 1 place
Script values 1
- court_chaplain_conversion_factors
Every has_game_rule = slower_faith_conversion_speed in game/common and game/events, by the top-level object it sits in.
slower_faith_conversion_speed

Source: game/common/game_rules/00_game_rules.txt line 892 (key faith_conversion_speed), modifiers from game/common/modifiers, names from the English localisation; Crusader Kings III 1.20.1.2.