PsychoPy loops parametrisation of 2 images variables

PsychoPy 3
Dear PsychoPy community ,

I am setting up an experiment with an image variable :
My loop go like this :
Cue + Fixation Cross + Image + ITI ( Interstimulus interval).

I have two variables of images :
Image 1 : Trigger pulses starting at 0ms ( Inner loop 1 )
Image 2 : Trigger pulses starting at 500ms ( Inner loop 2 ) ,

I put an outer loop grouping these two inner loops and woud like them to run randomly.

Tha image file contain 50 images, I want half of them to be set up with pulses starting at 0 and another half starting at 500ms, all in a randomised way.

Issue : My images are either displaying twice with both of trigger pulse’s types or running in a sequential loop showing images without randomization.

Is there any way to randomise my images ( linked to the trigger pulses) , OR randomise the trains of pulses starting time within the images since it is the same images files .

I have tried both of theses :

Find attached my experiment :
The final goal is to randomise the starting time of the pulses trains within one block.

PS: By Triggers or pulses I mean here paralele port component signal to start a trains of pulses on the TMS .
Thank you in advance for helppp.