Hi Andrew,
Hokkien characters are still very flexible (maybe that's going to be different, 10, 20 years down the road?) - I've seen 互, 予, 與 for the word 'h07' and 的, 個, ㄟ, 丌, 耶 and 兮 for e5. I tend to use 個 only for the measure word for months as in 後個月, 'next month' (兮 is kind of neat, because it doesn't look too bad and has no association with the individual functions of Mandarin 的 and 個, but not many people seem to use 兮).
For most of the function words there a similar dilemma, as they do not correspond 1:1 to the Mandarin equivalent - which shows nicely that Hokkien is more than a 'dialect'.
I do have a list of favorites that took me a while to figure out:
pronunc. ------ meaning ----- favorite character ---- [Mandarin pronuncitation]
a2, ia2 ------------- or ------------------- 抑 -------------------------- yi2
a2, iao2 -------- not yet ---------------- 猶 -------------------------- you2
ia2, iah8 ---------- also ----------------- 也 -------------------------- ye3
bo5 ----------------- not ----------------- 無 -------------------------- wu2
be7 --------------- not yet -------------- 未 -------------------------- wei4
m5 ------------------ not ----------------- 伓 -------------------------- bei1
bue7 ---------- to not know --------- [勿會] ------------------------ N.A.
khah4 ------------- more ---------------- 較 -------------------------- jiao4
kouh4 ------------- even ---------------- 佫 -------------------------- ho2
kap4 --------------- and ----------------- 合 -------------------------- he2
sim2mih8 --------- what --------------- 甚物 ------------------------ shen2wu4
li2, lu2, ly2 -------- you ----------------- 汝 -------------------------- ru3
i1 -------------------- he ------------------ 伊 -------------------------- yi1
gun2 ------------- we (excl.) ------------ 院 -------------------------- yuan4
cit4 ------------------ this ----------------- 此 -------------------------- ci3
hit4 ------------------ that ---------------- 彼 -------------------------- bi3
beh4 ---------------- want --------------- 慾 -------------------------- yu4
tioh8 ------------ correct, must --------- 著 -------------------------- zhu4
ti7 ------------------- in, at --------------- 在 -------------------------- zai4
I'm only putting them here as a suggestion for others that might have the same problem. Whoever know more, please comment

!
Regards,
Aurelio
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