Updates in response to feedback from Bhijn. Also adding in missed icons from my first sweep and renamed _corecross.dm to __corecross.dm.

code/__DEFINES/obj_flags.dm

@@ -25,6 +25,7 @@
 #define NOBLUDGEON				(1<<7)		// when an item has this it produces no "X has been hit by Y with Z" message in the default attackby()
 #define NODROP					(1<<8)		// This flag makes it so that an item literally cannot be removed at all, or at least that's how it should be. Only deleted.
 #define ABSTRACT				(1<<9) 	// for all things that are technically items but used for various different stuff
+#define IMMUTABLE_SLOW          (1<<10) //When players should not be able to change the slowdown of the item (Speed potions, ect)
 
 // Flags for the clothing_flags var on /obj/item/clothing
 

code/modules/research/xenobiology/crossbreeding/_clothing.dm

@@ -132,7 +132,7 @@ Slimecrossing Armor
 	icon_state = "adamsuit"
 	item_state = "adamsuit"
 	flags_inv = NONE
-//	obj_flags = IMMUTABLE_SLOW //Commented this out as Citadel currently lacks the IMMUTABLE_SLOW obj_flag.
+	obj_flags = IMMUTABLE_SLOW
 	slowdown = 4
 	var/hit_reflect_chance = 40
 

code/modules/research/xenobiology/crossbreeding/_weapons.dm

@@ -7,7 +7,7 @@
 	item_state = "bloodgun"
 	lefthand_file = 'icons/mob/inhands/weapons/guns_lefthand.dmi'
 	righthand_file = 'icons/mob/inhands/weapons/guns_righthand.dmi'
-	item_flags = ABSTRACT | DROPDEL
+	item_flags = ABSTRACT | DROPDEL | NODROP
 	w_class = WEIGHT_CLASS_HUGE
 	force = 5
 	max_charges = 1 //Recharging costs blood.
@@ -15,10 +15,6 @@
 	ammo_type = /obj/item/ammo_casing/magic/bloodchill
 	fire_sound = 'sound/effects/attackblob.ogg'
 
-/obj/item/gun/magic/bloodchill/Initialize()
-	. = ..()
-//	add_trait(TRAIT_NODROP, HAND_REPLACEMENT_TRAIT) //Commented out because Citadel lacks add_trait, TRAIT_NODROP and HAND_REPLACEMENT_TRAIT.
-
 /obj/item/gun/magic/bloodchill/process()
 	charge_tick++
 	if(charge_tick < recharge_rate || charges >= max_charges)

code/modules/research/xenobiology/xenobiology.dm

@@ -840,7 +840,7 @@
 		return
 	if(isitem(C))
 		var/obj/item/I = C
-		if(I.slowdown <= 0)
+		if(I.slowdown <= 0 || I.obj_flags & IMMUTABLE_SLOW)
 			to_chat(user, "<span class='warning'>The [C] can't be made any faster!</span>")
 			return ..()
 		I.slowdown = 0