I've checked with Forestry & Land Scotland and there is no work planned in the Fetteresso in May which might impact the challenge. SSEN are currently doing some work upgrading the powerlines that cross South to North but they don't seem to be causing any disruption to the trails and the work is planned to be finished during April.
https://www.ssen-transmission.co.uk/projects/project-map/east-coast-400kv-ohl-upgrade/
Note parts of the Forest, especially to the West near the Cairn O'Mount Road and near the TV mast are privately owned forest not managed by F&L Scotland.