Commerce - variant URL param
Not sure how you're outputting the url to the variant itself, but you can always create your own link and change the variant paramater to whatever you want.
Something link this: {{product.url}}?keywordyouwanttouse={{variant.purchasableId}}
On your product page you can then check if the url has the parameter and get the data of that variant.
I use the following code at the top of my product template and then use the selectedVariantto display sku, images, prices, ...
Here I use the variant querystring but you can change that to whatever querystring paramater you want to use.
{% set variantId = craft.app.request.getQueryParam('variant') ?? false %}
{%  if variantId %}
    {% set selectedVariant = craft.variants.id(variantId).one() %}
{% else %}
    {% set selectedVariant = product.defaultVariant %}
{% endif %}