weaken become weaker; "The prisoner's resistance weakened after seven days"
modify,
alter,
change make less severe or harsh or extreme; "please modify this letter to make it more polite"; "he modified his views on same-gender marriage"
vitalise,
vitalize make more lively or vigorous; "The treatment at the spa vitalized the old man"
ruggedise,
ruggedize produce in a version designed to withstand rough usage; "Detroit ruggedized the family car"
substantiate solidify, firm, or strengthen; "The president's trip will substantiate good relations with the former enemy country"
