I don’t believe items support a “looks-like” field. 2 options here, afaik, make and submit a new tile for them to your preferred tileset or change the existing tileset to assign a sprite to the cooked versions or wait for someone to do either of those things. Ok, 3 options…
I’ve attempted to fix my local copy of DeadPeople and managed to break it several times…can’t help here as of yet.
edit: After a crash course in tilesets…I searched for wild_veggy in my tileconfig.json and copied and edited the lines for the wielded and loose versions, then changed the entry for each item added by fiddleheads.
I’ve got a local fix for DeadPeople that makes them look like wild veggies. You’ll need to open up the tileconfig.json in your MSX++DeadPeopleEdition folder and insert the following lines where indicated. tileconfig.json is over 3mb in DP, not gonna upload the whole thing for 6 entries. 
Summary
Insert at line 24299
{
“id”: “overlay_wielded_fiddlehead_raw”,
“fg”: 1368,
“rotates”: false
},
{
“id”: “overlay_wielded_fiddlehead_boiled”,
“fg”: 1368,
“rotates”: false
},
{
“id”: “overlay_wielded_fiddlehead_sauteed”,
“fg”: 1368,
“rotates”: false
},
Insert at line 70854
{
“id”: “fiddlehead_raw”,
“fg”: 1368,
“rotates”: false
},
{
“id”: “fiddlehead_boiled”,
“fg”: 1368,
“rotates”: false
},
{
“id”: “fiddlehead_sauteed”,
“fg”: 1368,
“rotates”: false
},
edit: PR Submitted