50 Turn Counterspy simply sets the turn count for any Counterspy operations to 50 (on Standard speed).
I haven't seen this posted elsewhere yet, so thought I'd post one of the more obvious mods.
You can cancel the operation by clicking the spy in the city/district.
The Machiavellianism policy will also reduce this.
50 Turn Counterspy 1.01
Increase turn count for Counterspy ops to 50 (on Standard speed)