reseed auto_increment to specific number?
This works, does that answer your question?

create table dbo.test (id int identity(1,1), value int);


declare @indexmaxt int = 9999,@indexmaxt2 int;
SET @indexmaxt2 = @indexmaxt+1;
DBCC CHECKIDENT ('dbo.test' , RESEED, @indexmaxt2);


insert into dbo.test(value) values(1);

select * from dbo.test;


Results:
id  10000
value
1