3302.  Application of chapter; powers of settlor.--This chapter shall govern the ascertainment of income and principal, and the apportionment of receipts and expenses between tenants and remaindermen, in all cases where a principal has been established with or, unless otherwise stated hereinafter, without the interposition of a trust; except that in the establishment of the principal provision may be made touching all matters covered by this chapter, and the person establishing the principal may himself direct the manner of ascertainment of income and principal and the apportionment of receipts and expenses or grant discretion to the trustee or other person to do so, and such provision and direction, where not otherwise contrary to law, shall control notwithstanding this chapter.