Across:
8 Charlemagne loses realm (‘Charlemagne’ loses ‘realm’ = chagne = CHANGE) to convert (CHANGE),
9 It’s not easy (HARD-) to open show (open ‘show’ = -S-) for trendy (-HIP) (HARDSHIP) Dire Straits (HARDSHIP),
10 The (the = ET-H) problem (= anagram indicator) involving college (-C-) (ETCH) – it might leave the wrong impression? (ETCH),
11 Doesn’t give up (-TRIES) running through Pakistan (INDUS- river) at the start (= positional indicator) (INDUSTRIES) with those on the estate (with those on the industrial estate = INDUSTRIES),
12 Scientist (BOFFIN) is away (-OFF-) in rubbishy spot (B-IN) (BOFFIN),
14 Bulldoze (shove/barge = BAR-GE) over tops of outstanding natural area (tops of ‘outstanding natural area’ = -ONA-) (BARONAGE) for noble folk (BARONAGE),
15 Backtracks on The Road to Damascus (CHANGES ONE’S MIND) with 8 across (‘change’ = CHANGE-) from unit (ONE -) in Titanic, for example (SS = -S -S), and 24 across (‘mind’ = MIND) (CHANGES ONE’S MIND),
18 Short feature (short feature/ factor = FACTO-) with tips from the utility man (tips from ‘the utility man’ = =TUM) (FACTOTUM) or jack of all trades (FACTOTUM),
20 Slow type (TURTLE) comes out of his shell every so often (TURTLE),
22 Drugs (SPEED) and wicked spirit (DEMON) (SPEED DEMON) for one of those annoying types in the fast lane (SPEED DEMON),
24 Amidst wisdom in developing (amidst ‘wisdom in developing’ = MIND) outlook (MIND),
25 Green (IMMATURE) museum (Irish Museum of Modern Art = IMMA-) opens terrace upstairs (opens ‘terrace upstairs’ = -TU-) with central (middle of) area (central ‘area’ = -RE) (IMMATURE),
26 Removes all traces (ERASES) of what 5 down does (an ‘eraser’ ERASES).
Down:
1 Got the (got the = GHETTO) crack (= anagram indicator) from one of the worst places (GHETTO),
2 It’s a measure (INCH) of the contents of porcelain china (contents of “porcelain china” = INCH),
3 Opposition (DEFIANCE) made (made) a fair amount of (half of) (half of ‘made’ = DE-) prospective partner (fiancé = -FIANCE) (DEFIANCE),
4 Summits on colonial hills and dales (summits on ‘colonial hills and dales’ = CHAD) in Africa (CHAD),
5 With no width in Harris Tweed (no “width” in “Harris Tweed” = arrsee = ERASER) you could clean up if you use this (ERASER),
6 Night-watchman (ASTRONOMER) spends a lot of time looking into space (ASTRONOMER),
7 Got a job (HIRED) on Top Gear (top “gear” = G-) with a foreign type (a = -UN) (HIRED GUN) having a shot at celebrity for the money perhaps (HIRED GUN),
13 What Sat-Nav is supposed to do (FIND THE WAY) or is that what you’d expect Trip Advisor to arrange? (FIND THE WAY),
14 CIA is not in Colombia (‘CIA’ is not in ‘Colombia’ = olomb = BLOOM) to be successful (BLOOM),
16 Pressure from local Garda (HEAT) Force (force = PUMP) (HEAT PUMP) is bound to raise the temperature (HEAT PUMP),
17 Held out (EXTENDED) for old partner (EX-) to get time (-T-) when it’s all over (-ENDED) (EXTENDED),
19 It (it = TI-) reflects (= reversal indicator) political party (Democratic Unionist Party (DUP = -D UP) seizing last opportunity (last ‘opportunity’ = -Y) (TIDY UP) to clean the mess in The House (TIDY UP),
21 Connected (LINKED) to fake (= anagram indicator) Kindle (Kindle = LINKED),
23 Heard (= homophone indicator) these are the cuts the butcher is selling (“meat” = “meet” = MEET) for the get-together (MEET),
24 Local beef (local beef/whinge = MOAN) from Oman (Oman = MOAN) butcher (= anagram indicator).