How to add outline to merged shape

Hello!
I’ve made bunch of animations for a client webpage.
Now they need a separate version for the dark mode. As the original art style has black outlines. They’d like me to add a unifying white outline to all art to make it look like a sticker.
I’m wondering if there is a quick solution to this as adding the extra outline to each object separately wouldn’t create the desired look. Unfortunately precomping all comp and adding Layer style in AE won’t work, as layer styles aren’t supported in Lottie. I’m wondering if there is maybe a way to add that extra outline by editing the Lottie code - like “precomping” everything and just adding another outline. The example attached isn’t the actual work, just a simplified example to illustrate what I need. In reality there are a lot more objects and sometimes the layer count reaches even 50~ objects, so I need an efficient solution.