Without a table alteration, you could do this (using Matt's fine test setup)...

--testing setup

create table #recipe (recipeID int identity(1,1) primary key, recipename varchar(200))

create table #recipeline(reclineID int identity(1,1) primary key, recipeID int, itemid int)

insert #recipe( recipename)

select 'chicken' union all

select 'pizza'

insert #recipeline(recipeid,itemID)

select 1,20 union all

select 1,34 union all

select 1,70 union all

select 1,50 union all

select 2,60 union all

select 2,13 union all

select 2,28

go

--===== Remember the current max recipe ID

DECLARE @MaxRecipeID INT

SELECT @MaxRecipeID = MAX(RecipeID)

FROM #Recipe

--===== Duplicate the rows in the Recipe table

SET IDENTITY_INSERT #Recipe ON

INSERT INTO #Recipe (RecipeID,RecipeName)

SELECT RecipeID = RecipeID + @MaxRecipeID,

RecipeName = RecipeName

FROM #Recipe

SET IDENTITY_INSERT #Recipe OFF

--===== Duplicate the rows in the RecipeLine table

INSERT INTO #RecipeLine(RecipeID,ItemID)

SELECT RecipeID = RecipeID + @MaxRecipeID,

ItemID = ItemID

FROM #RecipeLine

--===== Display the results

SELECT * FROM #Recipe

SELECT * FROM #RecipeLine

--===== Cleanup the demo code

DROP TABLE #Recipe, #RecipeLine

Now, tell us why you want to do this, please? Thanks...