(define-syntax p-init #f)
(define-rename-transformer-parameter p (make-rename-transformer #'p-init))

#lang racket

(require racket/stxparam)
(define-syntax p-init #f)
(define-rename-transformer-parameter p (make-rename-transformer #'p-init))

(define-syntax (test-2-p stx)
  (syntax-case stx ()
    [(_ body)
     #'(with-syntax ([tmp #'(foo 123)])
         (syntax-parameterize ([p (make-rename-transformer #'tmp)])
           body))]))
(test-2-p #'p) ; #<syntax:10:28 (foo 123)>