Missing the Big Picture
by Kegler

In nine cases, Down entries overwrite one letter of intersecting Across entries.  The unclued entry at 30 Across
describes these overwritten letters, read in clue order.   The unclued entry at 8 Down describes the overwriters.

Across 1 Plans finish in a good time 8 Burrowing animal's bill cut back 12 Upset, Mr. Reiner returns around the... 13 ...first of October; oh, wow! 14 Beguiles with vacant poses after five in the morning 16 Felt sorry for rude crackpot 17 Reportedly dined with one after seven 18 Per Rev. Spooner, hear Ms. Remick's descriptor for unsupervised children 20 Scared of a loud attack 22 Screech owl in grove exhibits loud crying 23 Collection includes Magritte's “Tranquil to the Extreme” 26 Therefore, that man accepts brief enclosure 27 Accompany in foreign sector 30 See instructions 33 Every peculiar ache 37 Zero in on enemies, somewhat 38 Besotted heir's engagement 40 Slice of toasted bread and fish 41 Pair of zealots found inside had initiated frat members 42 Alien pilot entering preserves for sea creatures 44 Pay couple of sailors to lay around front of resort 45 Empty page breaks editing command 46 Large number in Michigan left one with pride? 47 Ceramic piece framing tenor's name 48 Calm, yet essentially turbulent sea 49 Island band guaranteed freedom 50 Uncovered shifting dune 51 New York baseball players eating large sandwiches 52 Animatedly hums “Go to the Dogs”?

Down 1 Side by side with an animal crossing river 2 Leave trace of unsightly hairs in stews 3 You and I captivated by end of the year spectacles 4 Preparing the wings: chopping finely, adding last bit of spice 5 Principal part of the foot 6 Footwear, and aprons missing scrap of muslin 7 Perform good flight without loss in sky battle 8 See instructions 9 Bury, however, abnormally large male 10 Chain letters 11 One strut supporting certain green facade 15 Heaters back by eastern platform 19 Tiny elastic nets I zip (hyph) 21 Made money maintaining dealer's car 24 Respond with extraordinary care and time 25 Surprisingly held rental “Spellbound” 28 Cruel dons mistreated scamp 29 Small dead plant 30 Greeted, come inside joint 31 Untwist the strands of a rope featured in royal nuptials' retrospective 32 Note sound of hesitation about dormitory's dangerous element 34 Beginner rebuilt cabined area 35 Drug company put iodine in source of sugar 36 Look, Marco redistributed storage space for wraps 39 Let Kate set off things that whistle 41 Dame Myra accepts a petite brooch with elation 43 Statute ethically providing effective means of enforcement

Solution