A quick update that may be relevant for future cards.
The news come primarily from Duel Links. The text for My Body as a Shield will be updated to remove the restriction from activating it during the Damage Step. (And yes, it will work that way, it’s not just to save space).
The latest TCG print and the (TCG) database entry for My Body as a Shield still list this restriction, so for now, play it as written until we get an update if you play in the TCG.
As a funny side note, My Body as a Shield hasn’t been reprinted in about 9 years in the OCG, so its text never explained that you cannot activate it during the Damage Step (it explained so in its rulings). Its most recent text was inside Duel Links:
The (OCG) official database has updated the rulings page for My Body as a Shield, explaining that it can now be activated during the Damage Step as well.
So you might be wondering if this is important if you don’t like using this card. It may be important for other cards as well: According to the Perfect Rulebook, effects that negate the activation of cards or effects can be activated during the Damage Step. This mostly allowed Monster Effects like Stardust Dragon to activate during the Damage Step. Counter Trap Cards in general can be activated during the Damage Step, so they were already allowed to be activated in this timing in the first place, whether they negated activations or not. This left out Spell Cards with Spell Speed 2 effects that negate activations and Normal/Continuous Trap Cards that negate activations outside of the group. This group of Spell and Trap Cards contains just a handful of cards that were usually individually ruled as not being allowed during the Damage Step. For a long time, this meant that you could only activate effects that negate activations during the Damage Step if they were Monster Effects or Counter Trap Cards.
Recently, Altergeist Protocol was released, and its effect is allowed to be activated during the Damage Step. Combining Protocol with this new ruling for My Body as a Shield, this may mean that we might get new Spell and Trap Cards in the future that negate activations, and those effects would be allowed during the Damage Step.