Pass image transformations into macro
Edit: I changed it to your variables, not sure if I set the array brackets 100% correct but the idea should work.

You could set the defaults in the macro as you already did, 
then in your template call the macro and pass the options e.g. :

{% set image = block.slide.first() %}
{# macro #}
  {% set imgParam = [
    thumb: { quality: 60, },
    tSM: { mode: 'crop', width: 1536 },
%}

{% macro isotopeItem(imgParam) %}


and merge the passed options in the macro with your macros defaults e.g.:

 {% set defaults = [
    thumb: { mode: 'fit', width: 100, quality: 60, },
    tSM: { mode: 'fit', width: 1536, quality: 80, },
    tMD: { mode: 'fit', width: 340, quality: 80, },
    tXL: { mode: 'fit', width: 1536, quality: 80, }
  ]
%}

{% set imgParam = imgParam ? defaults|merge(imgParam) : defaults %}


so you will only need to pass explicit changes.