Quick 'n' dirty way to expose simple means to set a representation's colorspace. Run this in admin console in tray launcher, then when opening tray browser it should show an action to "Change Representation Colorspace" - use the OPTION BOX to set a new one.

ayon_load_set_representation_colorspace.py

import ayon_api
from ayon_core.lib import TextDef, UILabelDef
from ayon_core.pipeline import register_loader_plugin, LoaderPlugin
from ayon_core.pipeline.colorspace import get_ocio_config_colorspaces
from ayon_core.pipeline.load import LoadError


class ChangeColorspaceLoader(LoaderPlugin):
    label = "Change Representation Colorspace"
    product_types = ["*"]
    representations = ["*"]
    order = 0.0

    color = "#FF0000"

    @staticmethod
    def _get_representation_colorspace(context) -> str:
        repre_data = context["representation"]["data"]
        colorspace_data: dict = repre_data.get("colorspaceData", {})
        return colorspace_data.get("colorspace", "")

    @classmethod
    def get_options(cls, contexts):

        # Current colorspace
        colorspace = ""
        for context in contexts:
            context_colorspace = cls._get_representation_colorspace(context)
            if context_colorspace:
                colorspace = context_colorspace
                break

        return [
            UILabelDef("Set colorspace name."),
            TextDef("colorspace",
                    tooltip="Colorspace to set.", default=colorspace)
        ]

    def load(self, context, name, namespace, options):

        print(options)
        if not options:
            raise LoadError(
                "No options were provided. Please use the Option Box."
            )

        # Set the representation colorspace data and apply with ayon API
        repre_data = context["representation"]["data"]
        colorspace_data: dict = repre_data.get("colorspaceData", {})
        if not colorspace_data:
            self.log.info(
                f"No colorspace data found for representation "
                f"'{context['representation']['name']}'. Skipping."
            )
            return

        colorspace: str = options.get("colorspace", "")
        if not colorspace:
            self.log.error("No colorspace value was provided in options.")
            return

        # Confirm the value does actually exist in the OCIO config
        ocio_colorspaces = get_ocio_config_colorspaces(
            colorspace_data["config"]["path"]
        )["colorspaces"]
        if (
                colorspace not in ocio_colorspaces
                and not f"role_{colorspace}" in ocio_colorspaces
        ):
            raise LoadError(
                f"Colorspace '{colorspace}' not found in OCIO config. "
                f"Available colorspaces: {', '.join(ocio_colorspaces)}"
            )

        if colorspace == colorspace_data.get("colorspace", ""):
            self.log.info(
                f"Representation '{context['representation']['name']}' "
                f"already has colorspace '{colorspace}'. Skipping."
            )
            return

        colorspace_data["colorspace"] = colorspace

        # Update representation data
        ayon_api.update_representation(
            project_name=context["project"]["name"],
            representation_id=context["representation"]["id"],
            data=repre_data
        )


register_loader_plugin(ChangeColorspaceLoader)