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Just pull back the mulch, do your planting, then return the mulch.

Temperatures in Batley do not require too many winter preparations. Maintain 5-10cm of organic mulch at all times of the year. Hydrangea roots are shallow, tiny, fibrous and they usually only grow about 10 cm deep or thereabouts. Thus, water if the soil feels dry at that depth. But avoid watering while temperatures are below freezing or if the soil freezes. Do not fertilize until you observe new growth in spring. Hydrangea macrophyllas should not be pruned this late in the growing season because they develop invisible flower buds at the ends of stems in late summer 2021/early fall 2021 and these buds then open in spring 2022. Thus, pruning stems now would result in cutting off spring 2022 blooms. Instead, prune -only if you need to- after they stop opening new blooms in 2022. At any time, you can deadhead spent blooms. You can also prune dead stems that do not leaf out by mid spring 2022. If you plant where the plant can attain its estimated size at maturity, you should not need to prune hydrangeas often. Miss Saori typically gets to be around 0.9 meter high/wide at maturity.

I would not use it. Make sure any mulch that you use is uncolored, untreated, and DO NOT use cedar mulch.

According to this extension article, it's not the color you should be concerned about but the wood. The coloring is non-toxic, but the wood used for colored mulch is scrap wood and could contain creosote.

https://nwdistrict.ifas.ufl.edu/hort/2019/05/17/is-colored-mulch-bad-for-the-environment/

You may want to skip the mulch altogether for your potting soil. You could use orchid mix if you have any on hand. It is basically bark.

If your soils are, already, moist then I would not put any mulch at all. This will provide breeding grounds for plant pathogens. Instead, I would opt for plants that thrive in moist areas, and leave the soil bare.

Lining the border with them would not be a bad idea, but they will, certainly be damaged by weathering over time.

https://www.gardeningknowhow.com/ornamental/water-plants/wgen/water-tolerant-plants.htm

We don't make product recommendations, and we don't have a related article, although we have one on using wool as mulch. You might check with your local Cooperative Extension Service because they are testing wool as fertilizer with good results.

https://www.gardeningknowhow.com/garden-how-to/mulch/mulching-with-wool.htm