Bam Margera 's ex is asking a judge not to change their custody arrangement ... claiming Bam's been in and out of their son's life in recent months -- and alleging in the order that he gave their son a roll-on device from his cannabis line, "BAM THC." Nikki Boyd filed the documents in court earlier this week in response to Margera asking a judge to grant joint legal custody of their 8-year-old son, Phoenix ... telling the court that Bam hasn't been as present a father in the last six months as