Workflow

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.