After creating your item set from your modular asset pack, there are two approaches to paint them as tiled level actor.
graph TD;
S[Item set]-->|Right click create asset| A[Tiled level asset];
S-->|Drag to level| Ins[Instanced tiled level actor];
A-->|Drag to level| AA[Asset tiled level actor];
AA-->|Convert to instance| Ins;
Ins-->|Promote to asset| A;
Tiled level asset #
An asset which stores your edits for a tiled level. It is feasible to reuse. Any edits made will reflect in all asset actors that use this asset.
Asset tiled level actor #
Click edit will open its source asset. Click convert to become instanced.
Instanced tiled level actor #
Click edit to directly edit it on level. You can also consider promoting it as an asset if you intend to reuse it elsewhere.